a 


Pear 


California 

egional 

acility 


--../  x 


UNIVERSITY  OF  CALIFORNIA 
AT   LOS  ANGELES 


GIFT  OF 

Citrus   Experiment 
Rj-.flt.1on 


U.  S.  DEPARTMENT  OF  AGRICULTURE, 

BUREAU  OF  ENTOMOLOGY— BULLETIN  No.  118. 

L.  O.  HOWARD.  Entomologist  and  Chief  cf  Bureau. 


THE   BEAN   THRIPS. 


II.  M.  RUSSELL, 

Entomological  Assistant. 


ISSUED  OCTOBER  16,  1912. 


WASHINGTON: 

GOVERNMENT    PRINTING 
1912. 


U.  S.  DEPARTMENT  OF  AGRICULTURE, 

BUREAU  OF  ENTOMOLOGY— BULLETIN  No.  118. 

L.  O.  HOWARD.  Entomologist  and  Chief  cf  Bureau. 


THE  BEAN   THRIPS. 


H.  M.  RUSSELL, 

Entomological  Assistant. 


ISSUED  OCTOHEK  16,  1912. 


WASHINGTON: 

GOVERNMENT  PRINTING  OFFICE. 
1912. 


BUREAU  OF  ENTOMOLOGY. 

L.  O.  HOWARD,  Entomologist  and  Chief  of  Bureau. 

C.  L.  MARLATT,  Entomologist  and  Acting  Chief  in  Absence  of  Chief. 

R.  S.  CLIFTON,  Executive  Assistant. 

W.  F.  TASTET,  Chief  Clerk. 

F.  H.  CHITTENDEN,  in  charge  of  truck  crop  and  stored,  product  insect  investigations. 

A.  D.  HOPKINS,  in  charge  of  forest  insect  investigations. 

W.  D.  HUNTER,  in  charge  of  southern  fleld  crop  insect  investigations. 

F.  M.  WEBSTER,  in  charge  of  cereal  and  forage  insect  investigations. 

A.  L.  QUAINTANCE,  in  charge  of  deciduous  fruit  insect  investigations. 

E.  F.  PHILLIPS,  in  charge  of  bee  culture. 

D.  M.  ROGERS,  in  charge  of  preventing  spread  of  moths,  fleld  ^vork. 

ROLLA  P.  CURRIE,  in  charge  of  editorial  work. 

MABEL  COLCORD,  in  charge  of  library. 

TRUCK  CROP  AND  STORED  PRODUCT  INSECT  INVESTIGATIONS. 
F.  II.  CHITTENDEN,  in  charge. 

H.  M.  RUSSELL,  C.  H.  POPENOE,  WM.  B.  PARKER,  H.  O.  MARSH,  M.  H.  HIGH, 

FRED  A.  JOHNSTON,  JOHN  E.  GRAF,  entomological  assistants. 
I.  J.  CONDIT,  collaborator  in  California. 
W.  N.  ORD,  collaborator  in  Oregon. 
THOMAS  H.  JONES,  collaborator  in  Porto  Rico. 
MARION  T.  VAN  HORN,  PAULINE  M.  JOHNSTON,  ANITA  M.  BALLINGER,  prcparators. 

2 


ADDITIONAL  COPIES  of  this  publication 
-£A-  may  be  procured  from  the  SUPERINTEND- 
ENT OF  DOCUMENTS,  Government  Printing 
Office,  Washington,  D.  C.,  at  10  cents  per  copy 


a* 

CO 


LETTER  OF  TRANSMITTAL 


U.  S.  DEPARTMENT  or  AGRICULTURE, 
CQ  BUREAU  or  ENTOMOLOGY, 

Washington,  D.  C.,  April  24,  1912. 

SIR  :  I  have  the  honor  to  transmit  herewith  for  publication  a  manu- 
N   script  entitled  "The  Bean  Thrips,"  by  H.  M.  Russell,  an  entomo- 
i    logical  assistant  of  this  bureau. 

v       This  bulletin  deals  with  an  insect  pest  of  the  family  Thripidae, 

<sJ  the  study  of  which  has  been  hitherto  largely  neglected,  and  which  of 

^  recent  years  has  attracted  considerable  attention  from  an  economic 

^  standpoint,  as  the  cause  of  immense  losses  in  the  Pacific  coast  regions 

?  and  elsewhere  to  truck  farmers.     The  insect  is  closely  related  to  the 

\  tobacco  thrips,  as  well  as  to  the  onion  thrips,  to  which  species  are 

•  t  chargeable  untold  losses  in  the  production  of  these  two  staples.     Ex- 

4  periments  to  produce  formulae  and  devices  with  which  successfully 

Nj^to  combat  this  insect  are  being  perfected,  and  methods  for  the  com- 

As  plete  control  of  the  pest  are  early  expected. 

I  recommend  the  publication  of  this  manuscript  as  Bulletin  No. 
(118  of  this  bureau. 

Respectfully,  L.  O.  HOWARD, 

Chief  of  Bureau. 
Hon.  JAMES  WILSON, 

Secretary  of  Agriculture. 

3 


243602 


CONTENTS. 


Page. 

Introduction 7 

Nature  and  extent  of  injury 8 

Description 8 

The  adult  female 9 

The  adult  male 10 

Recently  emerged  adults 10 

The  egg 10 

The  first-stage  larva 10 

The  second-stage  larva 11 

The  young  nymph  or  prepupa 12 

The  full-grown  nymph  or  pupa 13 

Origin  and  distribution 14 

History 16 

Recent  records 16 

Habits  of  the  adult 17 

Method  of  mating 17 

Method  and  time  of  oviposition 18 

Number  of  eggs  and  period  of  oviposition 19 

Proportion  of  the  sexes 20 

Kinds  of  reproduction 20 

Feeding  habits 20 

Flight 21 

Leaping 22 

Normal  length  of  life 22 

Length  of  life  in  winter 22 

Habits  of  the  larva 23 

Hatching 23 

Molting 25 

Habits  of  the  prepupa  and  pupa 26 

Food  plants 27 

Beans 27 

Other  vegetables 28 

Pear 28 

Alfalfa 28 

Cotton 30 

Wild  plants 30 

Seasonal  history  at  Compton,  Cal 31 

The  egg. , 31 

The  larva 32 

The  prepupa  and  pupa 34 

Total  life  cycle 36 

Emergence  from  hibernation 36 

Entrance  into  hibernation 36 

Number  of  generations 37 

5 


0  THE    BEAN    THKIPP. 

Page. 

Seasonal  history  in  the  Imperial  Valley 37 

Egg  period 37 

Larval  period 38 

Prepupal  and  pupal  periods 38 

Seasonal  history  at  Tempe,  Ariz 33 

Hibernation 39 

Notes  on  occurrence 40 

Natural  control 40 

Rains 40 

Natural  enemies 41 

Artificial  control 42 

Cultural  methods 42 

Spraying 43 

Distributing  the  parasites 44 

Bibliography 44 

Index...  47 


ILLUSTRATIONS. 


Page. 

FIG.  1.  Side  view  of  the  head  of  a  thrips,  showing  the  mouthparts 8 

2.  The  bean  thrips  (Heliothrips  fasciatus) :  Adult  female  and  details 9 

3.  The  bean  thrips:  Eggs 10 

4.  The  bean  thrips:  First-stage  larva 11 

5.  The  bean  thrips:  Second-stage  larva 12 

6.  The  bean  thrips:  Prepupa 12 

7.  The  bean  thrips:  Pupa 13 

8.  Map  showing  present  known  distribution  of  the  bean  thrips  (Heliothrips 

fasciatus) 15 

9.  Alfalfa  showing  injury  by  the  bean  thrips 29 

10.  The  bean  thrips:  Prepupse  parasitized  by  Thripoctenus  russelli 41 

11 .  A  hymenopterous  parasite,  Thripoctenus  russelli:  Adult 42 


THE  BEAN  THRIPS. 

(Heliothrips  fasciatus  Pergande.) 


INTRODUCTION. 

In  the  State  of  California  during  the  past  four  or  five  years  the 
bean  thrips  has  been  reported  with  increasing  frequency  as  a  serious 
pest  to  various  crops.  The  common  name  "  bean  thrips  "  is  somewhat 
of  a  misnomer,  as  this  insect  feeds  on  many  different  crops,  but  is  re- 
tained here,  as  it  is  well  known  by  that  name  in  California.  That 
State,  with  its  long,  dry  summer,  furnishes  climatic  conditions  un- 
usually favorable  to  the  development  of  thrips,  and  several  species 
have  gained  such  a  foothold  there  as  annually  to  cause  a  loss  of  hun- 
dreds of  thousands  of  dollars. 

In  the  summer  of  1909,  Mr.  R.  S.  Woglum,  of  the  Bureau  of  En- 
tomology, informed  the  author  that  during  the  summer  before  he  had 
seen  hundreds  of  acres  of  beans  in  southern  California  so  seriously 
infested  by  the  bean  thrips  that  they  had  the  appearance  of  plants 
scorched  by  fire;  and  as  this  thrips  seemed  to  be  increasing  in  num- 
bers and  destructiveness  it  appeared  to  be  the  part  of  wisdom  to 
obtain  all  possible  information  concerning  its  life  history  and  control 
before  it  reached  the  enormous  abundance  of  the  destructive  pear 
thrips  (Eutkrips  pyri  Daniel).  When,  therefore,  the  Bureau  of 
Entomology  established  a  field  station  at  Compton,  Cal.,  in  Septem- 
ber, 1909,  for  the  study  of  truck-crop  ard  sugar-beet  insects,  the 
writer  planned,  among  other  projects,  to  undertake  as  complete  a 
study  of  this  insect  as  time  would  permit.  With  this  in  mind,  the 
bean  thrips  has  been  the  subject  of  thorough  investigation  during  the 
years  1910  and  1911.  During  this  time,  however,  the  insect  was  not 
again  so  destructive  to  beans,  so  that  remedies  with  spray  mixtures 
could  not  be  thoroughly  tested.  Nevertheless,  as  the  life  history  has 
been  worked  out  and  a  large  fund  of  information  obtained  on  the  dis- 
tribution and  habits  of  this  thrips,  together  with  knowledge  of  a 
natural  enemy  of  some  promise,  this  paper  is  published  at  the  present 
time. 

At  Compton,  in  Los  Angeles  County,  where  the  life  history  of  this 
insect  was  studied  by  the  writer,  the  temperature  is  quite  cool,  since 
the  location  is  near  the  coast. 

7 


8  THE   BEAN    THRIPS. 

In  the  Imperial  Valley  the  life  history  of  the  bean  thrips  and  its 
injuries  to  alfalfa  and  cotton  have  been  investigated  by  Mr.  V.  L. 
Wildermuth,  of  this  bureau,  and  where  his  observations  are  used 
credit  is  given  in  the  text.1  Use  has  been  made  of  observations, 
by  Messrs.  P.  R.  Jones  and  S.  W.  Foster,  of  this  bureau,  on  this  insect 
in  the  more  northern  points  in  the  State.  Since  July,  1911.  the  writer 
has  been  ably  assisted  by  Mr.  John  E.  Graf.  He  also  wishes  to  ex- 
press his  appreciation  to  Dr.  F.  II.  Chittenden,  under  whose  direc- 
tions he  has  conducted  the  investigation,  and  to  Prof.  F.  M.  Webster 
for  the  free  use  of  notes  obtained  by  his  agents. 

NATURE   AND   EXTENT   OF   INJURY. 

The  damage  caused  by  the  bean  thrips  is  not  confined  to  the  foliage, 
but  affects  as  well  the  fruit  and  stems  of  the  plant  attacked.  The 
injury  is  caused  by  the  method  of  feeding. 
Both  young  and  adults  obtain  their  food  by 
puncturing  the  leaf  tissue  with  their  sharp 
mouthparts  and,  after  lacerating  it,  with- 
drawing the  plant  juices  at  the  point  of 
attack.  Figure  1,  although  a  drawing  of  a 
different  species,  gives  an  idea  of  the  mouth- 
parts  of  this  insect. 

Each  time  as  the  contents  of  the  leaf  at 
the  point  attacked  are  removed,  the  thrips 
moves  to  a  new  point  and  repeats  the  opera- 
tion, so  that  if  the  insects  are  abundant  or 
the  attack  is  long  continued  the  leaf  tissue  is 
showing     destroyed  over  the  entire  surface.     As  the 
the  mouthparts:   Much  en-     sllpplv  On  one  side  of  the  leaf  is  exhausted 

larged.      (After  Moulton.)     •        *  \  "  . , 

the  larva?  move  around  to  the  other,  or  if 

adults  are  present  these  fly  or  jump  to  more  tender  leaves.  The 
infested  and  badly  injured  leaves  turn  yellowish  or  white,  dry  up, 
and  either  drop  off  or  hang  lifeless  to  the  plant.  Then,  as  the 
attack  continues,  successive  leaves  are  attacked  until  in  extreme 
cases  the  entire  plant  is  killed. 

DESCRIPTION. 

Heliothrips  fasciatus  belongs  to  the  Suborder  Terebrantia  and  the 
Family  Thripida?  of  the  Order  Thysanoptera,  being  placed  in  this 
position  15ecause  of  the  downward-curved  ovipositor  of  the  female. 
The  8-segmented  antenna?,  with  the  last  segment  much  longer  than 
the  Tth,  and  the  reticulated  surface  of  the  body,  together  with  the 
pointed  spines  on  the  wings,  place  this  insect  in  the  Genus  Helio- 

*Mr.  Wildermuth  studied  the  insect  in  its  relation  to  alfalfa,  without  knowing  that  It 
was  being  investigated  by  the  author.  His  studies,  made  under  quite  different  climatic 
conditions,  add  materially  to  the  value  of  the  results  obtained. 


DESCRIPTION. 


9 


thrips.  The  habits  of  the  larva  are  also  quite  characteristic  of  this 
genus,  for  the  habits  of  the  larvae  of  the  greenhouse  thrips  (Helio- 
//</•//>*  hvemorrhoidalis  Bouche)  and  of  Heliothrips  rubrodnctus 
Giard  are  almost  identical  with  those  of  the  present  species. 


THE   ADULT  FEMALE. 


The  adult  female  (fig.  2)  is  about  one-twenty-fourth  of  an  inch 
in  length  (0.9815  mm.  to  1.1174  mm.;  average,  1.0405  mm.)  and 
about  one-fourth  as  wide  as  long  (0.2265  mm.  to  0.2869  mm.;  average 


Via.  2.— The  bean  thrips  (Ueliothnps  fasciatm)  :  a,  Adult  female ;  6,  ventral  side  of 
abdominal  segment  of  same;  c,  antenna  of  same,  a,  Greatly  enlarged;  6,  c,  more 
enlarged.  ^(Original.) 

width,  0.2529  mm.)  and  is  fusiform  in  shape.  The  head  and  body 
are  black  and,  under  the  microscope,  are  seen  to  be  covered  with 
distinct  reticulations  and  short  white  hairs.  The  antennae  are  8- 
segmented  and  two  and  one-half  times  as  long  as  the  head,  and  are 
held  out  in  front  of  the  body.  They  are  black,  more  or  less  banded 
with  white,  and  bear  white  hairs.  The  wings  are  held  folded  to- 
gether down  the  middle  of  the  dorsum;  they  are  black,  crossed  by 
a  white  band  at  the  base  and  a  white  band  at  three-fourths  the  dis- 
tance from  the  base.  The  wings  are  fringed  with  long  white  hairs. 
The  legs  are  black,  banded  with  white.1 

1  For  a  detailed  description  of  tho  genus  and  the-  species  for  use  of  systematists,  S«-P 
Hinds's  "Monograph  of  the  Thysanoptera  "  (Proc.  U.  S.  Nat.  Mus.,  vol.  26,  1902),  pp. 
174-175. 

51097°— Bull.  118—12 2 


10  THE   BEAN    THKIPS. 

THE  ADULT  MALE. 

The  male  resembles  to  a  great  extent  the  female,  as  the  color 
and  the  markings  are  the  same,  but  it  is  noticeably  smaller  in  size 
and  apparently  more  active.  When  viewed  under  the  microscope 
the  sexual  organs  are  seen  to  be  distinctly  different,  and  in  light- 
colored  or  cleared  specimens  the  testes  may  be  seen  as  two  orange-red 
bodies  in  the  abdomen,  and  on  the  middle  of  each  of  segments  2  to  6 
on  the  ventral  side  are  yellowish  oval  spots.  The  total  length  of 
the  male  is  0.7097  mm.  to  0.8002  mm. ;  the  average,  0.7474  mm.  The 
greatest  width  across  the  mesothorax  is  0.1963  mm.  to  0.2114  mm. ; 
the  average,  0.1978  mm. 

RECENTLY  EMERGED  ADULTS. 

Both  sexes,  when  just  emerged,  have  the  head  and  thorax  a  light 
yellowish  orange,  with  the  eyes  and  ocelli  bright  red.  The  antennrc 
are  white  and  ringed  with  brown,  while  the  wings  are  dusky,  crossed 
by  bands  of  a  darker  color.  The  legs  are 
white,  with  ends  of  each  segment  more  or  less 
black.  Gradually  the  color  darkens,  and  in 
a  day  they  all  have  the  fully  matured  colors, 
as  described  above. 


FIG.  3.— The  bean  thrips :  The  egg  (fig.  3)  is  bean  shaped,  0.21  to 
enlarged'  0.255  mm.  in  length  and  0.105  to  0.12  mm.  in 
width,  and  is  very  delicate  and  thin  shelled. 
It  is  translucent  white,  with  a  smooth  shining  surface.  The  eggs  are 
laid  in  the  tissue  of  the  leaf  or  in  the  veins,  or  even  in  the  stems,  and 
in  case  of  beans  may  be  laid  in  the  pods  themselves.  As  the  embryo 
within  develops,  the  egg  becomes  swollen,  and  the  little  pocket  in 
which  it  is  inserted  becomes  raised  above  the  leaf  surface.  The  eggs 
may  be  seen  in  the  leaf  tissue  if  examined  with  a  hand  lens  before 
the  light.  Each  little  egg  pocket  stands  out,  because  of  its  lighter 
color,  and  within  the  crude  outline  of  the  egg  may  be  seen. 

The  younger  stages  of  this  insect  differ  distinctly  from  those  of 
Heliothrips  hcemorrhoidalis  *  in  the  dashes  of  crimson  so  generally 
present  on  the  sides. 

THE  FIRST-STAGE  LARVA.2 
(Fig.  4.) 

Length,  0.42  mm. ;  width"  of  mesothorax,  0.135  mm.  General  shape  fusiform, 
similar  to  Heliothrips  hcemorrhoidalis;  head,  antennae,  and  legs  large  in  propor- 

1  For  description  of  Hcliotlirips  hcemorrhoidalis,  see  "  The  Greenhouse  Thrips,"  Bui.  64, 
Part  VI,  Bur.  Ent.,  U.  S.  Dept.  Agr.,  pp.  46-48,  1909. 

»  Description  made  while  larva  was  very  young  and  before  feeding  commenced. 


DESCRIPTION. 


11 


tiou  to  rest  of  the  body.  Color  traiisJuceut  white.  Head  large,  quadrate;  eyes 
reddish ;  ocelli  absent.  Antennae  0.195  mm.  in  length,  apparently  7-segmented ; 
basal  segment  cylindrical,  short;  second  nearly  twice  as  long  as  first,  barrel- 
shaped;  third  and  fourth  spindle-shaped,  ringed  with  a  few  fine  hairs;  fifth, 
sixth,  and  seventh  slender,  nearly  equal  in  length.  Legs  translucent  white. 
Abdomen  tapering  posteriorly ;  first  eight  segments  nearly  equal  in  length,  last 
two  segments  longer  than  others ;  each  abdominal  segment  with  longitudinal 
rows  of  setae,  the  tenth  with 
four  setae  about  0.045  mm.  in 
length. 

At  this  stage  there  seems  to 
be  nothing  to  distinguish  this 
species  from  H.  hoemorrhoidalis. 

THE  SECOND-STAGE  LARVA. 
(Fig.  5.) 

Length.  1.05  mm. ;  width  of 
mesothorax,  0.27  mm.  Shape 
fusiform,  about  same  as  larva ; 
of  mesothorax  and  meta  thorax 
long,  robust,  cylindrical;  sides 
of  mesothorax  and  metathorax 
and  first  five  abdominal  seg- 
ments nearly  parallel ;  pro- 
thorax  narrowed  toward  head ; 
last  five  abdominal  segments 
tapering  to  the  last  segment, 
which  is  cylindrical  and  trun- 
cated at  end.  Color  of  head 
and  pro  thorax  light  yellow, 
mesothorax  and  metathorax 
and  first  six  segments  of  abdo- 
men translucent  white,  stained 
on  sides  with  crimson  blotches 
and  with  yellow  on  dorsum  to 
some  extent;  next  three  seg- 
ments of  abdomen  the  color  of 
head,  last  segment  of  abdomen 
white;  alimentary  tract  plainly 
indicated  by  the  brownish  color 
given  it  by  inclosed  food.  Surface  of  body  covered  with  minute  granulations. 
Head  quadrate,  rounded  in  front  and  notched  behind  the  eyes,  0.12  mm.  long, 
O.OS25  mm.  wide ;  eyes  small,  reddish ;  ocelli  absent.  Antennae  7-segmented,  first 
four  segments  the  color  of  head,  the  others  translucent-  white;  first  segment 
short,  cylindrical;  second  longer,  barrel-shaped;  third  and  fourth  spindle-shaped 
'and  annulated;  fifth,  sixth,  and  seventh  slender  and  cylindrical.  Legs  long, 
yellowish.  Abdomen  0.60  mm.  in  length,  fusiform,  ovipositor  not  formed;  seg- 
ments with  rows  of  fine  setu^  increasing  in  length  toward  posterior  end;  ninth 
and  tenth  segments  with  longer  setae. 


FIG.  4.  —The  bean  thrips  :  First-stage  larva.     Greatly 
enlarged.      (Original.) 


12 


THE    BEAN    THKIPS. 


THE  YOUNG  NYMPH  OR  PREPUPA. 
(Fig.  6.) 

Length,  1.02  ram.;  width  of  mesothorax,  0.255  mm.  Shape  fusiform,  similar 
to  adult.  Head,  length,  0.09  mm. ;  width  at  eyes,  0.157  mm.  Head  translucent 
white,  vertex  slightly  yellowish,  ocelli  absent.  Head  rounded  in  front,  slightly 
notched  behind  the  eyes;  eyes  red,  made  up  of  a  few  facets,  surface  faintly 
reticulated ;  two  pairs  of  setse  behind  the  eyes  and  two  pairs  between  the  eyes. 
Antennae  translucent  white,  extending  forward,  0.195  mm.  in  length;  segments 
indistinct  but  apparently  7-segmented. 

Prothorax  about  one-half  again  as  wide  as  long,  sides  rounded,  posterior  edge 
broadest,  semitranslucent  white  to  yellow,  posterior  angles  tinted  with  crimson. 


PIG.  5. — The  bean  thrips  :  Second- 
stage  larva.  Greatly  enlarged. 
(Original.) 


FIG.   6.  —  The    bean    thrips:    Prepupa. 
Greatly  enlarged.     (Original.) 


setae  around  margin.  Mesothorax  with  rounded  angles,  translucent  white  to 
faint  yellow,  sides  and  posterior  angles  tinted  with  crimson,  wing-cases  trans- ^ 
parent  white,  distinct  from  each  other,  those  of  forewings  extending  to  middle 
of  second  abdominal  segment  and  those  of  hind  wings  extending  to  middle  of 
third  abdominal  segment.  Legs  strong,  translucent  white. 

Abdomen  fusiform  as  in  adult,  translucent  white  to  faint  yellowish,  edges 
with  tint  of  crimson,  which  enlarges  to  fair-sized  blotches  on  sides  of  seventh 
and  eighth  segments;  number  of  longitudinal  rows  of  setse  increasing  in  length 
toward  posterior  end.  Length  of  abdomen,  0.62  mm. 


DESCRIPTION. 
THE  PULL-GROWN  NYMPH  OR  PUPA. 


13 


(Fig.  7.) 

Length,  0.99-1.09  mm. ;  width  at  mesothoracic  angles,  0.24-0.255  mm  Shape 
similar  to  that  of  adult.  Color  orange;  posterior  border  of  prothorax 
mesothoracic  angles,  sides,  and  abdominal  segments  2,  3,  6,  and  7  more  or  less 
crimson.  Head,  length,  0.11  mm. ;  width,  0.18  mm. ;  orange,  apparently  faintly 
reticulated ;  eyes  dark  red,  larger  than  in  prepupal  stage,  facets  small.  Three 
ocelli  present  in  close  triangle  between  eyes,  in  color  yellow.  Antenna*  laid 
backward  on  head  and  reaching  to  beyond  middle  of  prothorax ;  segments  in- 
distinct, translucent  white; 
segments  1  and  2  projecting 
in  front  of  the  head  and  2 
with  four  setae  or  hairs,  two 
extending  forward,  about 
0.0135  mm.  in  length.  Tho- 
rax light  orange  or  yellow. 
Prothorax  about  twice  as 
wide  as  long.  Wing-cases 
0.54  mm.  long,  extending  to 
seventh  abdominal  segment, 
translucent  white.  Length 
from  head  to  end  of  wing- 
pads,  0.825  mm.  Legs  trans- 
lucent white.  Abdomen 
fusiform,  similar  to  adult, 
surface  plainly  reticulated 
in  older  specimens,  seta? 
well  developed,  the  longest 
ones  at  posterior  end. 
Length  of  abdomen, 
mm. ;  width,  0.31 
length  of  posterior 
O.OS5  mm. 

The  younger  stages  of  this 
insect  differ  distinctly  from 
those  of  11.  hcemorrhoidaUs* 
in  the  dashes  of  crimson  so 
generally  present  on  the 
sides. 

The  pupa  of  the  male 
is  shorter  and  more  slen- 


0.612 
mm. ; 
seta?, 


PIG.  7.— The 


Greatly    enlarged. 


der  than  that  of  the  fe- 
male. This  pupa  differs 
from  H.  hcemorrhoidalis  in  its  smaller  size,  in  its  yellow  color,  with 
the  sides  of  the  abdomen  more  or  less  stained  with  crimson,  and  in 
having  the  hairs  of  the  body  longer  and  the  second  segment  of  the 
antennae  with  two  long  setae. 

The  foregoing  descriptions  are  for  the  parts  of  California  in  Los 
Angeles   County  and  more  northern  points,  for  Mr.  Wildermuth 

1  For  description  of  Heliothrips  fuemorrhoidrilis,  see  "  The  Greenhouse  Thrips,"  Bui.  04. 
Part  VI,  Bur.  Ent.,  U.  S.  Dept.  Agr.,  pp.  46-48.  1909. 


14  THE   BEAN    THRIPS. 

found  that  the  different  stages  in  the  Imperial  Valley  lacked  the  red 
markings  except  in  the  cooler  weather  of  the  late  fall. 

ORIGIN  AND  DISTRIBUTION. 

This  insect  was  first  described  by  Mr.  Theodore  Pergande  from 
specimens  taken  in  Yuba  County,  Cal.  A  few  years  later  he  identi- 
fied a  thrips  from  Lewiston,  Idaho,  as  this  same  species. 

Mr.  Dudley  Moulton  reported  that  this  species  had  been  collected 
in  Colusa  County  by  Mr.  E.  K.  Carnes,  in  Santa  Rosa  County  by 
Mr.  O.  E.  Bremner,  and  in  the  Santa  Cruz  Mountains,  Santa  Clara 
County,  by  himself.  Mr.  D.  L.  Crawford  recorded  fasciatus  from 
Santa  Paula,  Ventura  County,  Cal.,  and  from  Claremont  arid  Chino, 
Cal.  Mr.  William  B.  Parker,  of  this  bureau,  collected  it  at  Davis  and 
Hamilton  City,  Cal.  Mr.  P.  R.  Jones,  engaged  in  pear  thrips  in- 
vestigations, reports  that  this  insect  occurs  very  commonly  around 
Lindsay  and  San  Jose,  Cal.  Mr.  S.  W.  Foster,  while  engaged  in  the 
same  investigation,  collected  this  insect  from  Martinez,  Cal.,  and  later 
found  it  "  frequently  throughout  Contra  Costa  County." 

Mr.  V.  L.  Wildermuth,  engaged  in  cereal  and  forage  insect  in- 
vestigations, has  collected  this  insect  in  California  at  Indio,  River- 
side County,  and  at  Bard,  El  Centre,  and  Holtville,  Imperial  County, 
and  in  Arizona  at  Yuma,  Yuma  County,  Buckeye  and  Tempe,  Mari- 
copa  County,  and  Sacaton,  Pinal  County. 

During  the  present  investigation  the  writer  has  collected  this  insect 
quite  extensively  from  many  places  in  southern  California.  In  1910 
it  was  found  to  be  very  abundant  on  wild  lettuce  in  several  yards 
and  alleys  in  the  city  of  Los  Angeles  itself.  At  various  times  it 
has  been  collected  from  Bell,  Compton,  Gardena,  Glendale,  Holly- 
wood, Laurel  Canyon,  Puente,  San  Gabriel,  Sierra  Madre,  Tropico, 
and  Whittier,  in  Los  Angeles  County.  In  Laurel  Canyon  the  author 
found  it  feeding  on  wild  food  plants  in  uncleared  land  about  6  miles 
from  cultivated  fields.  It  was  also  collected  near  the  entrance  of  the 
canyon,  scattered  over  the  mountain  sides  on  various  wild  plants.  At 
Sierra  Madre  it  was  taken  at  an  elevation  of  750  feet. 

It  was  also  collected  at  Garden  Grove,  Huntington  Beach,  Smelt- 
zer,  and  Sunset  Beach,  in  Orange  County,  Cal.  While  on  a  trip  in 
October,  1910,  the  author  found  this  insect  to  be  generally  distributed 
throughout  the  town  of  Oxnard,  and  in  Mental vo  and  the  entire 
outlying  sugar-beet  district  of  Ventura  County. 

In  February,  1911,  the  author  made  a  trip  to  San  Diego  to  investi- 
gate the  conditions  in  reference  to  truck  crops  there,  and  in  Mission 
Valley — a  long,  narrow,  and  fertile  valley  lying  to  the  north  of  San 
Diego,  and  devoted  to  truck  crops — this  insect  was  found  feeding  to 
some  extent  on  pea  vines.  The  writer  left  California  for  Washing- 
ton, D.  C.,  in  September,  1911,  and  while  delayed  at  Sparks,  Nev., 
he  examined  several  clumps  of  wild  lettuce  growing  along  the  rail- 


ORIGIN   AND  DISTRIBUTION.  jg 

road  track  and  collected  both  larval  and  adult  forms  of  th,  I,,,,,, 
thnps  upon  this  plant. 

tl  ^  Ai;  *'  ^iT^'f  thiS  bUreaU'  reC6ntly  reP°rted  to  the  wri*er 
that  he  had  collected  the  species  on  October  10,  1910,  at  Clarksville. 

*T'r7  thlS  mS6Ct  is  S0  widely  distributed  in  all  parts 

of  California  seems  to  point  strongly  to  that  State  as  its  original 
home.  This  is  also  strongly  supported  by  the  fact  that  Moulton 
collected  it  from  wild  vetch  in  the  Santa  Cruz  Mountains  and  that 
the  writer  collected  it  in  wild,  uncultivated  tracts  in  the  mountains 
and  canyons  north  of  Los  Angeles,  5  and  6  miles  from  cultivated 
crops.  This  point  of  view  is  further  strengthened,  because  the  au- 
thor has  found  this  insect  feeding  on  more  than  20  native  wild 
plants. 


FIG.  8. — Map  showing  present  known  distribution  of  the  bean  thrips  (Ilelio1hrii>x  }iiK,-iiHux\. 

(Original.) 

Mr.  J.  D.  Hood,  formerly  of  the  office  of  the  State  entomologist 
of  Illinois,  recently  informed  the  writer  that  he  possessed  specimens 
of  this  thrips  that  were  collected  by  Prof.  Lawrence  Bruner  at 
Lincoln,  Nebr.,  February  14,  1899,  and  that  he  had  collected  this 
same  species  at  Urbana,  111.,  in  March,  1907.  In  both  cases  the 
thrips  were  taken  on  California  oranges  and  had  evidently  been  cur- 
ried across  the  country  while  hibernating  in  the  navel  end  of  the 
fruit.  This  is  an  excellent  illustration  of  how  this  insect  may  be 
distributed  through  the  agency  of  man. 

Although  this  insect  is  quite  minute  and  has  been  little  studied, 
at  the  present  time  it  is  known  to  occur  through  the  entire  State  of 
California,  in  several  places  in  Arizona,  in  Nevada,  and  in  Idaho 
near  the  Washington  State  line.  It  has  also  been  found  in  one 
locality  in  Tennessee.  Figure  8  has  been  prepared  to  show  the 
present  definite  localities  where  this  insect  has  been  observed. 


16  THE   BEAN   THRIPS. 

Without  doubt  this  insect  occurs  over  the  entire  Pacific  coast  of 
the  United  States  and  down  into  Mexico  for  some  distance  and  pos- 
sibly even  into  Central  America.  As  it  becomes  better  known  it 
will  probably  be  found  to  occur  in  several  of  the  other  Western 
States  and  some  of  the  Eastern  States  as  well. 

HISTORY. 

In  1895  Mr.  Theodore  Pergande  (I)1  described  this  species  from  one 
specimen  received  from  Yuba  County,  Cal.,  where  it  was  taken  on 
an  orange  leaf  infested  with  (Aspidiotus}  Chrysomphalus  aurantii 
Mask.  At  that  time  he  expressed  the  opinion  that  the  occurrence 
on  this  plant  was  accidental.  In  view  of  our  present  knowledge, 
however,  of  the  feeding  habits  of  this  insect,  this  specimen  was 
probably  feeding  on  the  foliage  of  the  orange  itself. 

In  1902  Hinds  (3)  redescribed  the  female  from  one  specimen  in 
the  collection  of  the  Bureau  of  Entomology.  At  that  time  he  wrote 
that  nothing  was  known  of  the  life  history. 

Miss  Daniels  (4),  writing  in  1904,  noted  the  occurrence  of  this 
thrips  in  California.  At  the  same  time  she  erected  a  new  genus  and 
species,  Caliothrips  woodworthi  (4),  for  the  male  of  Heliothrips 
fasciatus.  This  error  was  first  pointed  out  by  Dudley  Moulton  (6) 
in  1907,  and  the  present  writer  agrees  with  him,  as  the  male  of 
fasciatus  fits  the  description  exactly  except  in  the  number  of. an- 
tenna 1  segments.  Undoubtedly  Miss  Daniels  made  a  mistake  in  the 
number  of  segments  in  the  antenna,  since  fasciatus  is  8-segmented  only. 

Crawford  (7),  in  1909,  under  "Notes  on  California  Thysanop- 
tera,"  records  taking  numerous  specimens  in  southern  California. 
These  were  captured  on  pine,  Lotus  glaber,  and  apple. 

Under  the  name  Euthrips  fasciatus,  Bremner  (8),  in  1910,  reported 
this  insect  as  injuring  beans  and  peas  and  as  occurring  on  alfalfa 
and  on  peach  and  pear  trees.  He  recommended  spraying  with  nico- 
tine solutions,  and  wrote  that  of  these  sulphate  of  nicotine  in  the 
proportion  of  1  ounce  to  5  gallons  of  water  had  given  perfect 
success. 

In  1911  Coit  and  Packard  (9)  wrote  that  the  bean  thrips  caused 
considerable  defoliation  to  cotton  and  alfalfa  in  Imperial  Valley,  Cal. 
Moulton  (10)  also  gave  a  list  of  its  food  plants. 

The  present  writer,  in  1911  (12)  and  also  in  1912  (13),  published 
two  papers  dealing  with  the  life  history  and  habits  of  Thripoctenus 
russelli  Crawf.,  a  parasite  reared  in  large  numbers  from  this  thrips. 

RECENT   RECORDS. 

This  species,  as  identified  by  Mr.  Pergande,  was  sent  to  the  Bureau 
of  Entomology  January  25,  1898,  by  Mr.  M.  J.  Wessels,  of  Lewiston, 

1  Numbers  in  parentheses  refer  to  the  Bibliography,  pp.  44-45. 


HABITS   OF    THE   ADULT.  J^ 

Idaho,  who  collected  it  in  a  diseased  spot  of  a  crab  apple.  On  Augi^t 
27,  1908,  Mr.  I.  J.  Condit  sent  in  specimens  of  this  thrips  from 
Davis,  Cal.,  where  they  were  injuring  sugar  beets.  He  wrote: 

I  examined  the  beets  and  found  them  literally  covered  with  thrips  both  tlu- 
surface  and  underside  of  the  leaves  being  badly  infested.  There  were  very 
few  leaves  which  were  not  attacked,  most  of  them  having  the  appearance  of 
the  specimens  sent.  A  field  of  tomatoes  near  by  was  also  becoming  infested 
The  lower  leaves  especially  were  yellow  and  some  falling  off. 

Mr.  S.  W.  Foster  informed  the  writer  that  on  August  26,  1900, 
Mr.  Frank  T.  Swett,  of  Martinez,  Cal.,  sent  to  the  laboratory  of 
the  Bureau  of  Entomology  at  Walnut  Creek,  Cal..  a  quantity  of 
pear  leaves  badly  injured  by  this  species.  On  August  31  Mr.  Foster 
visited  the  orchard  and  found  the  injury  quite  noticeable.  He  wrote 
that  "  the  foliage  gave  the  appearance  from  a  distance  of  having 
been  scalded."  Mr.  V.  L.  Wildermuth,  of  this  bureau,  sent  speci- 
mens taken  on  alfalfa  at  Indio,  Cal.,  on  July  2,  1910.  Mr.  A. 
McLachlan,  of  Davis,  Cal.,  sent  in  specimens  of  this  thrips  on 
October  13,  1910,  with  the  report  that  they  were  injuring  the  buds 
and  tips  of  cotton. 

Mr.  W.  B.  Parker,  of  this  bureau,  under  date  of  August  25,  1911, 
sent  this  insect  from  Davis,  Cal.,  with  the  statement  that  it  was 
causing  serious  damage  to  the  foilage  of  the  sugar  beet.  He  also 
collected  it  on  sugar  beets  at  Hamilton  City,  Cal.,  on  September  18, 
1911,  where  it  was  causing  some  injury.  He  wrote,  however,  that 
owing  to  the  lateness  of  the  season  when  the  beets  were  attacked 
probably  only  slight  damage  resulted. 

HABITS  OF   THE  ADULT. 

For  a  short  time  after  emerging  from  the  pupa  this  insect  remains 
quiet  and  appears  to  be  waiting  for  its  limbs  to  harden.  During 
this  time  the  colors,  which  were  light  at  emergence,  gradually  darken. 
After  hardening  the  thrips  moves  off  and  begins  feeding. 

METHOD   OF  MATING. 

The  males  and  females  of  this  species  seem  to  emerge  from  the 
pupa  at  about  the  same  time.  During  this  investigation  it  was  ob- 
served that,  under  laboratory  conditions  at  least,  the  sexes  mated 
generally  in  from  two  to  three  days  after  emergence  and  in  some 
cases  in  even  less  time.  This  operation  has  been  observed  both  in 
the  field  and  in  the  laboratory  and  was  identical  under  both  condi- 
tions. This  is  probably  best  described  by  the  original  field  notes 
made  at  the  time  of  observation. 

51097°— Bull.  118—12 3 


18  THE   BEAN    THKIPS. 

The  male,1  when  inclined  to  copulate,  picks  out  a  female,  and  if 
she  is  moving  over  the  leaf  runs  after  her  and  jumps  or  alights  on  her 
back.  In  some  cases  he  then  spreads  the  wings  and  moves  them  up 
and  down,  at  the  same  time  moving  the  tip  of  the  abdomen  in  the 
same  manner.  In  other  cases  the  male,  after  leaping  onto  the  back 
of  the  female,  remains  motionless  for  some  time  in  that  position.  It 
then  exserts  the  copulatory  organs  from  the  tip  of  the  abdomen  and 
shifts  around  toward  the  side  of  the  female,  at  the  same  time  bend- 
ing the  abdomen  under  to  the  ventral  side  of  that  of  the  female.  The 
copulating  organs  are  then  moved  back  and  forth  until  they  en- 
counter those  of  the  female.  In  some  cases  observed,  when  the  male 
did  not  succeed  in  connection,  it  would  withdraw  to  its  former  posi- 
tion on  the  female  and  after  remaining  quiet  for  a  short  time  would 
move  over  and  attempt  the  act  on  the  opposite  side.  As  soon  as  con- 
nection is  made  the  male  remains  motionless  for  a  short  time,  during 
which  period  the  female,  in  many  cases,  craAvls  slowly  around  on 
the  leaf.  After  a  few  minutes  the  male  relinquishes  his  hold  with 
the  copulating  organs  and  moves  squarely  back  onto  the  dorsum  of 
the  female.  Soon  after  the  male  crawls  off  and  away  from  the  female. 
This  entire  operation  was  observed  in  three  cases  to  occupy  3,  5,  and 
10  minutes.  Several  cases  were  observed  where  two  males  attempted 
copulation  with  the  same  female,  but,  after  a  vain  attempt,  one 
general!}7  left  her. 

METHOD    AND    TIME   OF   OVIPOSITION. 

Exactly  how  much  time  elapses  between  copulation  and  oviposition 
was  not  observed,  but  probably  not  more  than  a  day,  so  that  the 
female  will  begin  oviposition  within  three  days  from  the  time  she 
emerges  from  the  pupa.  In  one  case  adults  emerged  on  July  19, 
1911,  and  eggs  were  laid  four  days  later. 

Oviposition  usually  takes  place  during  the  night,  but  has  been 
observed  at  2,  3,  and  4.30  in  the  afternoon.  A  female  engaged  in 
oviposition  was  observed  to  crawl  over  the  leaf  of  the  food  plant 
for  a  short  distance  and  then  to  stop  and  scrape  a  hole  in  the  leaf 
with  her  mouth  cone.  This  was  accomplished  by  a  slight  forward 
and  backward  motion  like  that  of  a  chisel.  In  a  short  time  the 
female  ceased  this  action  and  moving  forward  until  she  could  place 
the  tip  of  the  abdomen  where  the  tissue  had  been  ruptured,  arched 
the  abdomen  in  the  middle,  arid  brought  the  tip  to  the  opening  in 

1  Pietro  Buffa  (Atti  Soc.  Toscano  Soc.  Nat.  Mem.,  vol.  23,  p.  48,  1907)  figures  JEolothrips 
fasciatus,  female  and  male  in  copulation,  in  a  position  identical  with  that  observed  by 
the  writer  in  Heliothrips  fasciatus  on  many  different  occasions. 

A.  F.  Shull  (A  Biological  Survey  of  the  Sand  Dune  Region  of  Saginaw  Bay,  Mich., 
pp.  190-192),  describing  copulation  in  the  suborder  Terebrantia,  expresses  doubt  as  to 
the  position  of  the  male  on  the  back  of  the  female  during  copulation.  As  his  observa- 
tions on  Euthrips  tritici  were  made  under  unfavorable  conditions  his  conclusions  were 
probably  erroneous. 


HABITS   OF  THE  ADULT. 


19 


the  leaf  surface.  She  then  proceeded  to  work  the  ovipositor  back 
and  forth  in  the  rupture  until  she  had  made  an  incision  of  sufficient 
depth.  After  this  she  became  motionless  for  a  varying  len«ih  of 
time,  while  the  egg  was  being  deposited,  whereupon  the  ovipositor 
was  removed,  and  the  female  moved  away. 

A  number  of  cases  have  been  observed  where  the  female  after 
inserting  the  ovipositor,  could  not  withdraw  it,  and,  thus  held,  she 
soon  died. 

NUMBER  01*  EGGS  AND  PERIOD  OF  OVIPOSITION. 

Owing  to  the  artificial  means  used  in  studying  the  habits  of  this 
insect  it  was  impossible  to  determine  exactly  how  many  eggs  a 
female  is  capable  of  laying.  However,  the  writer  confined  T  fe- 
males in  a  vial  for  observation.  They  laid  an  average  of  35.5  egg« 
each,  while  the  highest  average  for  any  day  was  5.5  eggs  each. 
Another  female,  during  the  period  from  August  16  to  August  23, 
1911,  laid  16  eggs,  the  greatest  number  laid  in  any  one  day  being  5. 
At  Compton,  Cal.,  during  1911,  females  kept  in  confinement  were 
observed  to  oviposit  for  30  days  in  succession,  while  others  were 
observed  to  oviposit  51  and  83  days  after  they  emerged  from  the 
pupae.  If  this  insect  normally  continues  oviposition  regularly  over 
a  period  of  83  days  the  total  number  of  eggs  laid  must  be  very  large. 

Mr.  V.  L.  Wildermuth,  while  in  the  Imperial  Valley,  made  some 
interesting  notes  on  the  number  of  eggs  this  species  may  deposit. 
On  August  2,  1910,  he  confined  2  females  on  leaves  of  alfalfa  in 
a  vial,  and  on  August  5  these  leaves  contained  50  eggs,  or  an  average 
of  25  eggs  each  in  3  days.  His  other  observations  are  given  in 
Table  I. 

TABLE  I. — Number  of  eggs  deposited  by  the  bean  thrifts  (Hcliothriiis  Jasciatus), 
Imperial  Valley,  Cal.,  1910. 


Ejtper- 
iment 
No. 

Date  female 
was  put  in  vial. 

Date  and  number  of  eggs. 

Total 
period  of 
oviposi- 
tion. 

Total 
number 
of  eggs. 

1910. 

Eggs. 

1910. 

Eggs. 

1910. 

Eggs. 

Dead. 

1 
2 
3 
4 

5 

1910. 
Aug.  29  
Aug.  31  
do  
do  

1911. 
Sept.  28  i  

Sept.    1 
Sept.    4 
Sept.    7 
Sept.    1 

Sept.  30 

36 
42 
53 
20 

12 

Sept.   2 

6 

Sept.    6 

37 

1  

**-, 

3 
6 

1 

46 

79 
42 
53 
30 

134 

Oct.     3 
Oct.  6\ 
Nov.    1 

25 

47 
27 

Oct.    11 
'Nov.'ii" 

24 
.... 

Record  made  at  Tempe,  Ariz. 


Iii  these  experiments  the  longest  period  of  oviposition  was  46  days, 
and  the  largest  number  of  eggs  laid  by  a  single  female,  134. 

It  will  be  observed  from  these  figures  that  the  females  observed  by 
Mr.  Wildermuth  deposited  more  eggs  and  at  a  more  rapid  daily  rate 


20  THE   BEAN   THRIPS. 

than  those  observed  by  the  writer.  This  may  have  been  due  to  the 
higher  temperature  of  the  Imperial  Valley  and  vicinity,  where  his 
observations  were  made.  Mr.  Wildermuth  noted  adults  in  copula- 
tion the  day  that  they  emerged,  and  oviposition  on  the  following 
date.  He  also  observed  this  species  to  oviposit  during  the  entire  day, 
whereas  the  writer  never  observed  it  to  oviposit  except  in  the  after- 
noon or  night. 

PROPORTION  OF  THE  SEXES. 

The  bean  thrips  was  under  the  observation  of  the  writer  for  a 
period  of  more  than  two  years,  during  which  time  it  had  been  ob- 
served in  the  field  at  all  times  of  the  year.  In  all  observations  made 
during  the  investigation  of  this  insect  the  males  and  females  were 
collected  together  and  copulation  was  observed  from  early  in  Febru- 
ary until  reproduction  ceased  late  in  the  fall.  Apparently  the 
females  outnumber  the  males,  but  this  may  be  due  to  the  fact  that 
the  females  are  not  quite  so  active  as  the  males,  and  are  not  dis- 
turbed on  the  plants  when  examined.  On  June  9,  1911,  out  of  17 
specimens  reared  in  the  laboratory  9  were  females  and  8  males.  July 
17,  1911,  the  writer  examined  another  series  of  live  adults  that  were 
reared  in  the  laboratory.  Out  of  10G,  80  were  females  and  2G  males. 
A  third  series  of  reared  adults  was  examined  October  16,  1911,  and 
out  of  4A  adults  32  were  females  and  12  males.  Apparently  the  per- 
centage of  females  is  too  high  and  does  not  indicate  the  exact  rela- 
tion between  the  sexes. 

KINDS   OF   REPRODUCTION. 

In  all  observations  made  on  this  topic  reproduction  has  been 
bisexual,  and  in  view  of  the  fact  that  males  were  observed  at  all 
times  and  copulation  also  occurred  at  all  times  in  the  year  when 
this  insect  was  active,  this  would  seem  to  be  the  usual  method.  How- 
ever, although  the  few  experiments  made  to  determine  whether 
parthenogenesis  occurred  gave  negative  results,  in  view  of  the  pre- 
ponderance of  females  during  certain  parts  of  the  season  it  is  quite 
probable  that  asexual  reproduction  may  occur.  It  would  seem  that 
this  method  would  occur  under  certain  conditions,  especially  in 
view  of  the  fact  that  the  greenhouse  thrips  (Heliothrips  hamorrhoi- 
dalis)1  reproduces,  so  far  as  we  know.,  asexually  only,  the  male  hav- 
ing never  been  discovered. 

FEEDING   HABITS. 

Both  the  adult  and  larva  of  this  thrips  injure  the  host  by  feeding 
on  the  foliage.  As  in  the  case  of  the  greenhouse  thrips,  the  lower 

1 "  The  Greenhouse  Thrips,"  Bui.  64,  Bur.  Ent.,  U.  S.  Dept.  Agr. 


HABITS   OF   THE  ADULT.  21 

and  earlier  leaves  are  first  attacked  in  the  spring  by  the  adults. 
These  feed  on  the  underside  of  the  leaves,  scraping  out  the  leaf 
content  in  small  spots  that  become  white  and  conspicuous.  Often 
the  adults  move  along  and  leave  a  chain  of  white  spots  to  mark  their 
progress.  The  adults  also  feed  to  some  extent  on  the  surface. 
As  they  feed  the  females  deposit  their  eggs  in  the  leaf  tissues,  and 
as  soon  as  incubation  is  completed  the  larva?  hatch  and  join  the 
adults  on  the  leaves.  Under  these  conditions  the  leaves  become  more 
or  less  dried  and  lifeless,  and  the  adults  move  to  the  higher  and  more 
tender  leaves  of  the  plant.  In  this  way  the  entire  plant  may  become 
infested.  On  February  5,  1911,  the  writer  found  the  adults  of  this 
insect  extremely  abundant  in  the  pea  field  of  some  Chinese  truckers 
at  Hollywood,  Cal.  Here  nearly  every  plant  had  7  or  8  adults  feed- 
ing on  the  underside  of  the  foliage,  and  in  many  cases  5  and  6  were 
present  on  each  leaf.  On  August  18  of  the  same  year  in  the  same 
locality  plants  of  spiny  wild  lettuce  (Lactuca  scariola)  were  observed 
that  had  50  adults  feeding  on  a  single  leaf. 

The  adults  seem  to  feed  on  a  large  variety  of  plants  and  have  been 
found  feeding  on  all  of  the  plants  given  under  "  List  of  food  plants." 
It  may  be  well  to  state  at  this  point  that  the  presence  of  adults  on  a 
plant  has  not  been  considered  sufficient  evidence  to  class  that  plant 
as  a  food  plant,  but  whenever  larvae  of  this  insect  were  taken  on  a 
plant,  this  was  considered  sufficient  to  rank  the  plant  as  a  host. 

In  the  spring  when  the  adults  leave  hibernation  they  collect  on 
the  wild  food  plants  present  and  feed  on  them  until  their  injury, 
due  to  an  increase  in  numbers  and  feeding,  weakens  the  plants  and 
shortens  the  food  supply;  then  they  fly  to  fresh  plants  of  the  same 
hosts  or  to  cultivated  crops  and  fruit  trees  nearby.  Of  all  the  food 
plants  observed,  the  spiny  wild  lettuce  (Lactuca  scariola}  seems  to 
be  the  most  favored.  This  plant  has  been  found  to  be  infested  more 
heavily  than  any  of  the  other  food  plants  concerned,  not  excepting 
those  of  economic  importance. 

FLIGHT. 

The  present  writer  in  his  investigations  of  the  greenhouse  thrips  > 
never  observed  that  insect  to  take  flight  naturally,  or  even  when  dis- 
turbed. The  adults  of  Heliothrips  fasciatus,  on  the  contrary,  take 
flight  very  readily,  and  if  jarred  or  disturbed  will  usually  fly  or  jump. 
This  species  in  taking  flight  raises  the  tip  of  the  abdomen  quickly, 
and  separates  the  wings.  It  then  rises  straight  up  into  the  air  and 
flies  rapidly  away  in  short  undulating  curves.  Indeed,  to  the  un- 
trained eye  it  appears,  in  flight,  exactly  like  a  small  speck  of  soot 
being  blown  around  by  a  slight  breeze.  This  power  of  flight  aids 
greatly  in  the  dispersion  of  this  insect  during  the  spring  and  summer. 


Loc.  cit. 


22 


THE   BEAN    THRIPS. 


This  species  possesses  the  power  to  leap  actively  and,  considering 
its  size,  to  a  considerable  distance.  It  is  no  uncommon  occurrence  for 
the  specimens  which  are  being  examined  upon  a  plant  to  leap  off  and 
be  lost.  Like  the  greenhouse  thrips,  it  will  crawl  over  the  leaves 
rapidly  when  disturbed.  At  other  times  it  will  remain  motionless 
for  a  considerable  period,  lying  closely  to  the  surface  of  the  leaf  along 
one  of  the  veins. 

NORMAL  LENGTH  OF  LIFE. 

The  length  of  life  of  this  insect  as  an  adult  has  been  determined 
under  the  artificial  conditions  of  confinement  in  vials  containing 
fresh  leaves  of  the  food  plant.  As  often  as  these  lost  their  freshness 
other  leaves  were  put  in  and  the  adults  were  changed  with  a  camel 's- 
hair  brush. 

Even  under  these  conditions  the  length  of  life  observed  for  some 
individuals  was  surprisingly  long,  when  we  consider  the  minute  size 
of  the  insect.  During  these  experiments  it  was  observed  that  these 
insects  were  very  sensitive  to  humidity  or  a  lack  of  it  and  all  were 
soon  killed  whenever  the  vials  used  in  confining  them  became  too  dry. 
Table  II  shows  the  results  of  these  experiments  in  which  some  thrips 
lived  for  84  days. 

TABLE  II. — Length  of  life  of  adult  ~bcan  thrips  a<t  Compton,  Cal.,  1911. 


Bate  adults  emerged  from  pupa. 

Number 
emerged. 

Specimens  died. 

Last 
adult 
died. 

Maximum 
length  of 
life. 

Date. 

Number. 

Days. 

April  Id  

3 

/Mav     8 
\May   11 

1 
1 

}May  22 

37 

May    8 

\           24 

April  2:$  

11 

Mav   18 

bulv   143 

' 

84 

May  26 

1 

June    5 

1 

J 

June  5  

0  '/June  17 
'    \June  21 

5 
3 

}Aug.  14 

71 

[July  22 

July  25 

2 

July  19  

14  Jjuly  26 
4  jlAup.    8 

2 

Aug.  21 

34 

Aug.  12 

2 

I  Aug.  17 

1 

Male  and  female. 


LENGTH  OF  LIFE  IN  WINTER. 


A  number  of  adults  were  collected  from  host  plants  on  November 
18,  1910,  and  were  placed  in  vials  and  furnished  with  fresh  leaves  at 
intervals,  and  some  lived  in  confinement  in  this  manner  until  Febru- 
ary 1, 1911,  by  which  time  all  had  died.  On  January  16, 1911,  a  num- 


HABITS  OF   THE   LARVA.  23 

her  of  adults  were  taken  from  the  open  on  leaves  of  nasturtium  and 
were  placed  in  vials.  These  died  in  April,  giving  a  length  of  life 
after  being  collected  of  92  days.  As  adults  have  never  been  ol».-rv,,l 
to  emerge  from  pupae  later  than  December  27,  these  adults  must  h;m- 
been  at  least  21  days  old  when  collected,  so  that  they  lived  about  113 
days.  Probably  hibernating  individuals  live  as  long  as  5  months. 


HABITS  OF  THE  LARVA. 


In  observing  the  habits  of  the  larva  of  this  thrips,  the  writer  was 
constantly  impressed  with  the  great  similarity  that  existed  between 
this  species  and  the  greenhouse  thrips.  This  is  so  great  that  the 
description  of  habits  of  the  one  would  almost  equally  fit  the  other. 

HATCHING. 

Apparently  the  hatching  process  may  occur  at  any  time  during 
the  day.  Many  have  been  observed  hatching  early  in  the  morning 
and  one  larva  was  observed  emerging  from  the  egg  cavity  at  4.25 
p.  m.  Very  slowly  this  larva  pushed  its  way  out  of  the  egg  cavity,1 
during  which  time  the  appendages  were  all  held  closely  appressed 
to  the  body  and  were  invisible.  As  soon  as  the  body  was  nearly  out 
the  insect  began  a  slow  forward  and  backward  movement  and  at 
4.40  p.  m.  all  but  the  tip  of  the  abdomen  was  free,  while  the  larva  pro- 
jected straight  out  from  the  leaf  surface.  While  held  in  this  position 
it  began  slowly  to  unfold  the  limbs  and  antenna?  and  move  them 
around.  The  motion  was  very  feeble  at  first,  but  gradually  the  larva 
seemed  to  gain  strength  and  at  4.48  p.  m.  it  bent  over  and,  grasping 
the  leaf  surface,  began  to  pull  with  its  limbs  in  order  to  free  itself. 
This  was  accomplished  at  4.53  p.  m.,  making  the  total  period  required 
in  emerging  from  the  egg  28  minutes. 

The  larvae  of  this  insect  after  hatching  move  away  a  short  distance, 
then  appear  to  rest  for  a  few  minutes  until  they  become  stronger. 
Within  a  short  time,  however,  they  move  on  and  soon  commence 
feeding.  When  first  hatched  the  larva?  are  very  minute  and  almost 
colorless,  but  as  they  begin  to  feed  and  drain  the  green  coloring 
matter  from  the  leaf  the  alimentary  tract  becomes  plainly  visible 
from  the  contained  food.  In  a  few  days  the  color  of  the  body 
becomes  more  or  less  yellowish  and  blotched  with  crimson.  In  com- 
mon with  other  species  of  Heliothrips,  the  larvse  of  the  present 
species  keep  the  tip  of  the  abdomen  elevated  and  carry  around  on  it 
a  small  globule  of  reddish  liquid  excrement.  Gradually  this  globule 
increases  in  size  until  it  is  too  large  to  be  carried  any  longer  ami  i' 
falls  to  the  leaf  surface.  Here  in  time  it  dries  and  forms  a  black 
spot  or  scale.  The  occurrence  of  these  spots  on  the  leaf  of  a  plant 

iThis  larva  emerges  from  the  egg  by  the  same  method  that  Is  used  by  the  conchuela 
(Pentatoma  ligata  Say)  as  described  by  Morrlll  (Bui.  8fi,  Bur.  Ent,  U.  S.  Dept.  , 
38-39). 


24  THE   BEAN    THKIPS. 

marked  by  feeding  of  some  thrips  furnishes  good  evidence  that  the 
bean  thrips  has  been  feeding  there  at  some  time.  The  larvae  feed  in 
much  the  same  manner  as  the  adult,  the  mouthparts  being  practically 
the  same.  They  gradually  scrape  out  the  contents  of  the  leaf,  leav- 
ing silvery  spots,  which  as  they  become  abundant  often  unite  and 
gradually  destroy  the  vitality  of  the  leaf.  Most  of  the  eggs  seem  to 
be  laid  on  the  underside  of  the  leaves,  although  the  writer  has  ob- 
served eggs  to  hatch  from  the  upper  side  also.  As  a  consequence 
the  larva?  begin  feeding  largely  on  the  underside  of  the  leaves.  After 
hatching  they  do  not  move  far  before  commencing  to  feed,  during 
which  time,  under  ordinary  conditions,  they  move  very  little.  When 
plants  are  first  infested  the  larva?  seem  to  feed  close  to  the  leaf 
veins,  but  as  the}7  become  more  abundant  they  scatter  in  groups  over 
the  entire  leaf  surface.  Like  those  of  the  greenhouse  thrips  the 
larvoe  of  this  species  seem  to  cluster  in  colonies  and  unless  disturbed, 
or  in  need  of  fresh  food,  remain  thus.  The  colonies  are  in  many  cases 
found  in  between  two  veins  of  the  leaves.  When  disturbed  the  lame 
will  violently  twitch  the  end  of  the  abdomen  with  its  drop  of  liquid 
and  move  away  rapidly.  Apparently  this  is  used  as  a  means  of  de- 
fense, for  the  writer,  in  work  with  a  parasite  of  this  thrips,  observed 
at  times  that  these  larva?  when  touched  from  in  front  by  the  parasite 
flung  the  abdomen  around  and  moved  rapidly  away.  When  this  oc- 
curred the  parasite  generally  retreated,  but  returned  to  the  attack 
and  later  usually  succeeded  in  ovipositing  in  its  host. 

The  larva?  and  adults  of  this  thrips  feed  together  in  colonies,  and 
as  the  leaves  become  crowded  or  dry  from  excessive  feeding  the 
larva?  move  in  search  of  fresh  food.  Gradually  the  whole  under- 
side of  the  leaf  attacked  becomes  infested  by  the  larva?  and  then 
the  surface  as  well.  In  fact,  the  writer  has  seen  leaves  so  heavily 
infested  by  the  larva?  of  this  thrips  as  to  give  them  a  decidecUy 
larva?  move  in  search  of  fresh  food  food.  Gradually  the  whole  under 
reddish  color,  due  to  the  bodies  of  the  insects.  So  far  this  larva 
has  not  been  observed  feeding  in  the  blossoms  of  any  plant, 
but  in  some  cases  it  has  been  observed  feeding  on  green  tomatoes, 
and  when  bean  vines  are  badly  infested  the  pods  are  also  attacked. 
Indeed,  when  excessively  abundant,  these  insects  will  not  only 
cover  both  sides  of  the  leaves^  but  the  stem  of  the  plant  as  well. 
The  larvae,  as  a  rule  feed  unprotected  on  the  leaf,  but  at  times  may 
be  found  feeding  under  the  protection  of  red-spider  webs. 

Apparently  these  minute  creatures  are  not  affected  by  dust,  as 
the  writer  has  found  them  feeding  in  large  numbers  on  leaves  of 
spiny  lettuce  in  an  alley  in  the  city  of  Los  Angeles  when  the  leaves 
were  so  thickly  covered  with  dust  as  completely  to  hide  the  surface. 
It  would  seem  that  with  the  enormous  clouds  of  dust  that  arise  in 
this  section  during  the  entire  summer,  completely  coating  the  larva?, 
they  would  speedily  succumb. 


HABITS   OF    THE    LARVA. 


25 


As  an  illustration  of  how  abundant  this  insect  may  become  the 
following  observations  are  given:  On  August  31,  1909  Mr  Foster 
of  this  bureau,  found  it  severely  infesting  pear  foliage  at  Martinez' 
Cal.,  and  noted  as  many  as  200  larvae  on  one  side  of  a  leaf.  On 
July  28,  1910,  the  writer  found  some  plants  of  spiny  lettuce  badly 
infested  by  the  larva?  of  this  thrips,  and  10  leaves  gave  a  total  infes- 
tation of  733.  (See  Table  III.)  This  gave  an  average  of  73  3  to  each 
leaf. 

TABLE  III.— Infestation  of  Lactuca  scariola  ly  larva  of  the  bran  thri,,*. 


No.  of 
leaf. 

Number 
of  larvae 
on  under 
side. 

Number 
of  larvae 
on  upper 
side. 

Total 
number  of 
larvae 
on  leaf. 

No.  of 
leaf. 

Number 
of  larvae 
on  under 
side. 

Number 
of  larva? 
o^unper 

Total 
number 
of  larva) 
on  leaf. 

1 
2 
3 
4 
5 

70 
34 
43 
30 
59 

7 
39 
2 
2 

47 

77 
73 
45 
32 
106 

7 
8 
9 
10 

44 
61 
70 
23 

47 
30 

1 
32 

91 
91 

71 
55 

6 

46 

46 

92 

480 

253 

733 

On  July  18,  1911,  at  Hollywood,  Cal.,  leaves  of  spiny  lettuce  were 
found  that  had  several  hundred  larva?  to  a  leaf.  September  22,  1910, 
Mr.  Wildermuth  observed  a  field  of  cotton  at  El  Centre,  Cal.,  show- 
ing considerable  injury  by  this  insect,  and  counted  as  many  as  200 
larvae  to  a  single  leaf. 

MOLTING. 

The  larva  molts  once,  giving  two  larval  instars,  then  molts  to  the 
prepupal  stage.  On  July  28,  1910,  a  number  of  larvae  that  had  just 
hatched  were  separated  and  on  August  2  these  all  molted.  On  August 
7  they  again  molted  and  changed  to  prepupae.  This  gave  the  first 
instar  a  length  of  five  days  and  the  second  a  length  of  five  days.  The 
process  of  molting  in  the  larva  is  continued  unprotected  in  the  midst 
of  the  feeding  colony.  After  molting  the  skin  is  left  adhering  to  the 
leaf  beside  the  feeding  larva. 

It  was  observed  with  the  larva?  of  this  species  and  of  those  of  the 
greenhouse  thrips  that  when  they  were  exposed  to  a  low  temperature 
the  entire  development  was  checked  and  growth  remained  stationary 
during  the  exposure.  In  long-continued  exposures  the  insect*  were 
killed,  but  if  within  three  weeks  they  were  again  removed  to  higher 
temperatures  the  larvae  resumed  their  growth  and  pupated  in  a 
few  days. 

Under  the  artificial  conditions  of  rearing  in  vials  the  mature 
larvae  seek  concealment  before  pupation  in  curled-up  leaves,  in  all 
kinds  of  protected  places,  and  if  in  vials  closed  with  cotton  plugs 
they  work  their  way  in  between  the  plug  and  side  of  the  vial.  In 
the  field,  however,  the  larvae  when  full  grown  desert  the  plants  and 
hide  in  rubbish  and  cracks  in  the  ground  or  beneath  clods  of  earth. 
51097°— Bull.  H8—12 4 


26  THE   BEAN    THEIPS. 

The  molting  from  larva  to  prepupa  under  laboratory  conditions  has 
been  observed  many  times.  On  April  10,  1911,  a  mature  larva  was 
observed  to  begin  the  process  at  4.05  in  the  afternoon.  After  remain- 
ing motionless  for  some  time  it  arched  its  body,  and  shortly  after 
the  skin  split  down  the  head  behind  the  antennae.  The  head  grad- 
ually forced  its  way  out  of  the  opening,  then  the  body  followed,  the 
old  skin  being  slipped  off  behind.  This  molting  was  completed  at 
4.21  p.  m. 

HABITS  OF  THE  PREPUPA  AND  PUPA. 

The  prepupae  of  this  insect  are  found  in  company  with  the  pupae 
and  full-grown  larvae  in  small  social  colonies.  These  hold  the 
antenna?  out  in  front  of  the  body  and  move  about  to  some  extent. 
The  pupas,  however,  carry  the  antennae  folded  back  on  the  head  and 
thorax  and  remain  motionless  unless  disturbed  or  exposed  to  the 
light,  in  which  cases  they  will  slowly  crawl  away.  When  com- 
pelled to  pupate  in  closed  vials  the  prepupa3  and  pupae  occur  in 
large  numbers  closely  packed  together  along  the  edge  of  the  vial 
and  the  cotton  plug  or  buried  in  the  cotton  itself.  In  nature  it  has 
quite  different  habits.  While  the  greenhouse  thrips  under  natural 
conditions  pupates  on  the  leaf  of  the  food  plant  in  among  the  feeding 
larva?,  with  the  bean  thrips  this  seldom  takes  place,  and  during  the 
two  years  this  species  has  been  under  observation  by  the  writer  only 
three  pupae  have  been  found  on  the  plants  infested  by  hundreds  of 
thousands  of  larvae.  In  one  case  a  pupa  was  found  under  the  web  of 
the  red  spider  near  the  midrib  of  a  leaf  of  spiny  lettuce ;  in  another, 
one  was  found  under  a  web  of  red  spider  on  a  leaf  of  the  wild  tobacco 
flower;  and  the  third  was  found  in  a  curled-up  lettuce  leaf. 

December  17,  1910,  a  quantity  of  the  dead  leaves  of  wild  helio- 
trope Avere  collected  on  the  ground  under  infested  plants.  Prolonged 
sifting  revealed  the  presence  of  a  single  pupa.  In  1911,  the  prepupae 
and  pupa?  were  found  by  Mr.  John  E.  Graf  and  the  writer  to  be 
very  abundant  in  infested  bean  fields  under  clods  or  lumps  of  dry 
earth  and  in  cracks  or  holes  in  the  lumps.  Upon  exposure  to  the 
light  these  at  once  began  to  move  away  in  search  of  darkness. 

Mr.  Wildermuth  also  found  the  pupae  of  this  insect  underground. 
He  wrote  in  his  notes  on  September  23 : 

While  searching  by  aid  of  a  binocular  for  pupae,  I  found  one  pupa,  one 
prepupa,  and  two  (mature)  larvae  just  at  the  crown  of  the  plant  and  beneath 
the  soil;  one  pupa  about  one-fourth  inch  below  the  surface  of  the  soil  in  an 
oval  cavity  about  three  times  as  long  as  the  pupa  itself;  one  prepupa  between  a 
dead  leaf  and  the  soil.  Never  have  I  found  a  pupa  above  the  surface  of  the 
ground,  on  the  leaves  of  the  plant,  or  between  the  sheath  leaves  and  the  stem, 
as  frequently  occurs  in  confinement. 

The  molting  of  the  prepupa  to  the  pupal  stage  is  very  similar  to 
that  described  for  the  change  of  the  larva  to  the  prepupa.  It  takes 


FOOD  PLANTS.  27 

place  in  whatever  location  the  prepupa  may  be,  and  the  transmit 
and  delicate  empty  skin  is  found  behind  the  pupa.  It  was  observed 
during  the  fall  that  pupae  exposed  to  a  low  temperature  did  not  com- 
plete  their  development  to  the  adult  stage.  These,  when  later  placed 
in  the  greenhouse,  changed  to  adults  unless  exposed  to  the  unfavorable 
conditions  too  long,  when  all  were  killed. 

During  the  pupal  stage  several  external  changes  take  place.  Vt 
first  the  ocelli  are  not  evident,  but  as  the  pupa  develops  these  become 
prominent  in  a  triangle  between  the  folded  antennae.  Then  the  reticu- 
lations of  the  body  begin  to  appear,  and  within  two  days  of  the 
emergence  of  the  adult  the  pupa  begins  to  darken  and  the  legs, 
antennae,  and  wings  begin  to  show  blackish  bands.  The  adult 
emerges  in  a  manner  similar  to  the  molting  of  the  larva.  Emerircncc 
has  been  noted  at  all  hours  of  the  day,  and  there  seems  to  be  ^"par- 
ticular time  for  its  occurrence. 

FOOD  PLANTS. 

This  insect  seems  to  be  nearly  as  omnivorous  as  the  onion  thrips. 
as  the  following  list  of  food  plants  upon  which  it  has  been  reared  <>r 
observed  during  the  past  two  years  by  the  writer  would  indicate. 
These  have  been  divided  into  economic  and  wild  food  plants,  and 
under  each  will  be  given  notes  on  injury  and  appearance  of  injured 
plants. 

BEANS. 

The  injurious  occurrence  of  this  insect  on  the  foliage  of  beans  <ri  ve- 
to it  its  common  name.  It  has  been  observed  by  the  writer  to  feed  on 
bean  foliage  in  the  adult  and  larval  stages  from  early  in  February, 
in  sheltered  places,  until  the  plants  a-re  killed  by  frost  in  the  fall. 
In  the  spring  the  wild  plants  are  first  up,  and  the  attack  is  largely 
concentrated  on  them,  so  that  when  the  beans  come  up  they  are  not 
immediately  attacked.  However,  in  a  few  weeks  the  insect  spreads 
to  the  beans,  thereafter  increasing  in  numbers  until  in  the  late  sum- 
mer and  fall  much  injury  is  done.  When  snap  beans  are  infested 
the  adults  first  attack  the  leaves,  and  while  feeding  lay  countless  rirgs 
in  the  tissue.  The  larvae  on  hatching  begin  to  feed,  and  gradually 
the  green  coloring  matter  is  entirely  removed  from  the  underside  «>f 
the  leaf.  This  becomes  white  and  covered  with  the  black  spots  of 
excrement.  The  infestation  then  spreads  to  the  surface  and  to  other 
parts  of  the  plant.  As  the  feeding  goes  on  the  leaves  lose  all  color, 
become  wdiite,  or  dry  up  and  turn  brown  and  drop  off.  As  the  infes- 
tation increases,  the  stems  and  pods  themselves  are  also  attacked  and 
ruined.  A  badly  infested  field  appears  as  if  scorched  by  fire.-  The 
lima  bean  and  pink  bean  suffer  in  the  same  way.  The  blackeye  cow- 
peas  this  past  season  were  almost  immune  from  the  attack  of  this 
insect,  even  in  fields  in  which  the  pink  beans  and  spiny  lettuce  were 
very  badly  infested. 


28  THE   BEAN    THEIPS. 

OTHER  VEGETABLES. 

During  the  spring  and  early  summer  this  insect  is  not  noticeable 
on  either  the  sugar  or  table  beets.  Late  in  the  summer,  however,  as 
the  wild  plants  die  down,  these  plants  often  become  badly  infested, 
but  as  the  beets  have  nearly  completed  their  growth  little  real  in- 
jury results.  The  outside  leaves  seem  to  be  first  infested,  showing 
series  of  minute  white  spots  more  or  less  in  chains,  where  the  chloro- 
phyll has  been  removed,  but  in  badly  infested  leaves  the  underside 
becomes  white  and  dried  and  covered  with  small  black  spots,  causing 
the  leaves  to  wilt.  Mr.  Parker  wrote  from  Hamilton  City,  Cal., 
under  date  of  September  18,  1911,  that  the  injury  was  apparent  in 
almost  every  field. 

Cabbages  and  other  crucifers  are  commonly  infested  by  this  thrips 
and  at  times  may  be  seriously  injured.  On  March  27,  1911,  cabbages 
in  the  laboratory  yard  were  slightly  infested.  Where  they  had  fed 
long  the  underside  of  the  leaf  was  full  of  the  silvery-white  feeding 
marks  of  this  insect  and  the  tiny  black  specks  of  excrement.  Cauli- 
flower suffers  to  the  same  extent  as  the  less  valuable  cabbage. 

This  insect  has  also  been  found  feeding  quite  extensively  on  let- 
tuce, potato,  and  tomato.  At  Hollywood,  Cal.,  in  February,  1911, 
it  was  very  abundant  on  the  foliage  of  pea  vines,  but  the  infestation 
did  not  appear  to  increase,  probably  because  the  vines  were  quite  old. 

PEAR. 

Mr.  S.  W.  Foster  found  pear  foliage  badly  injured  on  August  31, 
1909,  at  Martinez,  Cal.  He  wrote: 

The  foliage  gave  the  appearance  from  a  distance  of  having  been  scalded. 
Close  examination  showed  that  the  leaves  were  often  injured  in  large  areas  on 
either  or  both  surfaces.  The  larvae,  feeding  only  on  these  outer  surfaces,  soon 
cause  the  blackened  areas. 

As  the  tree  has  made  most  of  its  growth  for  the  season  and  the  fruit  crop 
has  been  harvested,  it  is  hardly  probable  that  this  species  will  prove  of  serious 
consequence  to  the  growers  unless  it  should  get  so  numerous  as  to  appear  in 
numbers  early  in  the  season. 


The  following  field  observations  on  the  work  of  the  bean  thrips 
on  alfalfa  and  cotton  were  made  by  Mr.  Wildermuth  in  the  Imperial 
Valley,  Cal.: 

August  2,  1910.  This  thrips  does  nearly  all  if  not  all  of  its  feeding  on  the 
upper  surface  of  the  leaf.  The  excrement  is  arranged  in  definite  rows,  often 
semicircular  in  form,  around  these  eaten  spots  and  makes  a  very  characteristic 
mark  [see  fig.  9].  The  eaten  spots  later  turn  yellow  and  then  the  alfalfa 
presents  a  sickly  appearance.  August  4  I  visited  several  alfalfa  fields  and  all 
were  very  much  injured  by  this  thrips.  Scarcely  a  leaf  could  be  found  that 


POOD  PLANTS.  29 

was  green  arid  fresh  as  it  should  be     TliP 


FIG.  9. — Alfalfa  showing  Injury  by  the  bean  thrips.      (Original.) 

of  attack.  September  30  the  fields  were  still  being  b.-ully  damaged.  After  a 
field  is  newly  irrigated  just  after  cutting  for  a  week  or  10  days  the  dnuuivo  is 
not  noticeable,  but  after  three  weeks  nearly  all  leaves  show  the  effects  and  tin- 
alfalfa  presents  a  very  sickly  appearance.  A  lack  of  sufficient  water  causes 
the  damage  to  be  more  noticeable,  as  under  such  a  condition  the  growth  of  the 
alfalfa  is  not  so  rapid  and  the  thrips'  damage  is  more  conspicuous. 


30  THE   BEAN    THEIPS. 

On  September  18.  1911,  he  wrote: 

This  thrips  is  very  abundant  in  alfalfa  fields  at  this  time  of  year,  the  larva? 
being  present  on  the  older  alfalfa  and  the  adults  present  on  the  younger  shoots 
and  leaves.  Many  leaves,  after  being  badly  scarred  by  the  thrips,  wilt  and  fall 
off,  so  that  the  damage  is  soon  very  great.  It  seems  rather  strange  that  this 
thrips  should  become  so  vary  abundant  in  the  fall  of  the  year  and  Euthripa 
tritici,  the  other  important  alfalfa  thrips,  should  decrease  in  numbers  and 
that  in  the  spring  of  the  year  just  the  opposite  should  be  the  case. 

COTTON. 

September  22,  1910,  Mr.  Wildermuth  wrote : 

This  thrips  was  found  damaging  cotton  about  11  miles  southeast  of  El 
Centre,  Cal.  The  cotton  was  only  damaged  in  one  corner  of  the  field,  and  it 
happens  that  fresh  alfalfa  is  being  stacked  close  to  this  corner. 

September  28  a  field  of  cotton  east  of  Imperial  had  a  strip  through  the  center 
of  the  field  damaged  by  this  thrips.  September  30  numerous  fields  on  the  east 
side  of  the  valley  were  being  damaged  by  this  pest.  The  leaves  were  dead  and 
rusty  looking  and  the  plants  in  bad  condition.  The  damage  was  not  as  great  as 
if  the  work  had  begun  earlier  in  the  season,  but  was  at  that  time  very  great. 

October  11  several  cotton  fields  at  Holtville,  on  the  east  side  of  the  valley, 
were  examined.  A  great  many  fields  showed  considerable  injury.  The  leaves 
were  eaten  and  turned  a  sickly  yellowish  or  brown,  many  often  being  curled. 
A  field  on  the  Young  ranch  was  as  badly  damaged  as  any  seen,  and  this  field 
lay  alongside  an  alfalfa  field.  Three  other  fields  on  the  same  ranch  showed 
very  little  damage.  The  former  field  was  of  a  late  planting.  This  thrips  has 
caused  much  more  damage  to  cotton  than  was  anticipated,  and  if  it  should 
begin  its  work  early  in  the  season  it  might  prove  extremely  destructive.  Be- 
cause of  this,  as  well  as  other  still  better  reasons,  cotton  should  be  planted  as 
early  as  possible  in  the  spring. 

In  November.  1911,  Mr.  Wildermuth  wrote: 

Mr.  Packard  and  cotton  growers  throughout  the  valley  report  but  little  injury 
to  cotton  by  this  thrips  this  year.  I  found  only  two  specimens  of  larvae  myself, 
and  a  few  adults.  It  would  seem  as  if  the  damage  to  cotton  coines  when  cotton 
follows  alfalfa.  This  year,  there  being  but  little  alfalfa  laud  put  *o  cotton 
and  more  cotton  following  cotton,  the  damage  was  not  so  noticeable. 

WILD   PLANTS. 

Of  all  food  plants  of  this  insect  the  wild  spiny  lettuce  (Lactuca 
scariola}  seems  to  be  preferred,  at  least  in  the  vicinity  of  Los  Angeles. 
From  early  spring,  when  this  plant  comes  up,  until  it  dies  down  in 
the  fall,  it  is  usually  badly  infested  by  thrips.  Many  cases  have  been 
observed  where  other  food  plants,  such  as  beans,  etc.,  in  the  same  field 
were  only  slightly  infested,  while  the  spiny  lettuce  near  by  was  so 
badly  attacked  that  many  plants  were  dead.  Furthermore,  this  weed 
is  one  of  the  commonest  in  the  country,  occurring  abundantly  in  un- 
cultivated or  even  in  badly  cultivated  fields.  In  addition  it  grows 
up  in  dense  clumps  in  all  fence  rows  and  roadsides,  and  the  rights 
of  way  of  the  different  railroads  are  densely  packed  by  this  plant. 


SEASONAL  HISTORY  AT  COMPTON,   CAL.  31 

When  this  weed  first  comes  up  in  the  early  spring  there  is  scarcely 
any  vegetation,  so  that  it  offers  an  agreeable  host  to  the  bean  thrips, 
especially  as  the  foliage  is  very  tender  and  juicy  at  that  time.  The 
thrips  attack  the  first  young  leaves,  and  the  larvae,  upon  hatching 
from  eggs  deposited  at  that  time,  join  the  feeding  adults.  As  soon 
as  these  become  abundant,  the  leaves  lose  all  or  nearly  all  of  the  green 
leaf-content  and  turn  white,  after  which  they  dry  up  and  hang  dead 
from  the  stalk.  The  infestation  continues  to  spread  to  the  younger 
leaves  until  the  entire  plant  is  killed. 

The  sow  thistle  (Sonchus  oleraceus)  has  the  same  general  distri- 
bution and  is  also  a  favorite  food  plant. 

Wild  heliotrope  (Heliotropium  curassavicum)  is  another  favorite 
food  plant  late  in  the  year.  This  plant  does  not  start  in  the  spring 
until  quite  late,  and  when  it  does  appear  above  the  ground  generally 
escapes  destruction  by  cultivation.  Thus  it  occurs  commonly  in  the 
beet  and  bean  fields  and  in  orchards,  and  in  the  fall  is  one  of  the 
chief  food  plants. 

The  bean  thrips  has  also  been  found  feeding  and  reproducing  in 
numbers  on  Euryptera  lucida  and  on  one  of  the  cucurbitacea?,  prob- 
ably an  Echinocystis,  in  a  canyon  north  of  Los  Angeles.  In  the  same 
locality  it  was  later  taken  feeding  and  reproducing  on  Gnaphalinm 
calif  ornicum,  Mirdbilis  californica,  Eunamis  brevipcs,  Chenopodimn 
murale,  Helianthus  annuus,  Atriplex  sp.,  wild  turnip,  Erigeron  cana- 
densis,  and  wild  pea  (Lotus  americanus} .  It  was  also  taken  in  the 
valleys  feeding  and  reproducing  on  the  Chinese  cigarette  flower  (Nic- 
otiana  glauca] ,  Bidens  pilosa,  Verbascum  virgatum,,  Polygonum  avi- 
culare,  and  Crepsis  (?)  sp.  The  adults  were  also  taken  in  the  fall 
feeding  on  the  foliage  of  a  porch  vine,  Tacsonia  mellissimus,  and  on 
the  cultivated  nasturtium  (Tropceolum  major}.  Mr.  A.  C.  Morgan 
found  it  on  the  underside  of  the  leaves  of  the  tulip  poplar  at  Clarks- 
ville.  Tenn. 

This  thrips  has  also  been  recorded  as  feeding  on  Lotu*  glalcr, 
apple,  peach,  orange,  wild  vetch,  burr  clover,  and  radish. 

After  perusal  of  the  above  list  of  food  plants  it  is  easy  to  see  how 
this  insect  can  obtain  a  foothold  in  a  cultivated  crop  in  the  late 
summer,  especially  as  many  of  the  wild  plants  die  from  maturity  or 
lack  of  moisture,  thus  forcing  the  insect  to  migrate. 

SEASONAL  HISTOBY  AT   COMPTON,   CAL. 

The  life  cycle  of  the  bean  thrips  was  observed  at  Compton  for  vary- 
ing parts  of  the  year,  and  because  of  the  cooler  and  more  even  tem- 
perature prevailing  there  is  quite  extended  and  more  nearly  equa 
for  the  entire  period  of  reproductive  activity. 

THE  EGG. 

The  length  of  time  required  for  the  egg  to  hatch  in  the  months  of 
March,  April,  and  May  was  not  exactly  determined.  However,  fr 


32 


THE    BEAN    THEIPS. 


leaves  of  wild  lettuce  were  collected  on  April  7  and  they  had  a 
number  of  eggs  in  them  very  recently  laid.  The  last  of  these  hatched 
on  April  24,  making  the  length  of  incubation  about  17  days,  or  possi- 
bly as  many  as  21  days.  The  average  mean  temperature  for  these 
21  days  was  59.1°  F. 

In  July  several  adults  of  this  thrips  were  confined  over  night  on 
leaves  of  growing  plants  that  were  uninfested,  and  were  removed 
on  the  following  morning.  In  this  way  a  number  of  eggs  were  ob- 
tained that  hatched  under  absolutely  normal  conditions,  ns  the  plants 
were  kept  in  an  open-air  insectary. 

Table  IV  has  been  prepared  to  show  the  records  of  incubation  for 
these  eggs. 

TABLE  IV. — Length  of  egg  stage  of  the  bean  thrips  in  July  at  Compton,  CaL,  191 J. 


Dates  eggs  hatched  and  number  each  day. 

Date  of 
ovipo- 
sition. 

First  egg 
hatched. 

Last  egg 
hatched. 

Shortest 
incuba- 
tion. 

Longest 
incuba- 
tion. 

Total 
eggs 
hatched. 

Julv 

Julv 

Julv 

July'  July 

July 

July 

July 

23. 

24. 

25. 

26. 

27. 

•28. 

29. 

30. 

July    10 

5 

54 

16 

3 

2 

6 

July  23 

Days. 
Julv  28               13 

Days. 
18 

M 

July    11 

26 

18 

9 

7 

July  24 

July  27               13 

17                  60 

July    14 

8 

15 

July  28 

July  29               13 

14                  23 

169 

In  this  experiment  169  eggs  hatched  and  the  minimum  length  of 
incubation  was  13  days  and  the  maximum  18  days,  but  nearly  50 
per  cent  hatched  in  just  14  days.  During  this  total  period  the  aver- 
age mean  temperature  was  69.6°  F. 

Again,  on  August  20  adults  were  confined  over  night  on  a  living 
plant  of  wild  lettuce,  and  4  larvse  hatched  on  September  4,  and  7  on 
September  5,  making  the  periods  of  incubation  15  and  16  days. 
During  this  time  the  average  mean  temperature  was  66.3°  F. 

During  the  months  of  October  and  November  the  incubation  is 
probably  lengthened  a  few  days  and  will  take  about  21  days,  as  the 
average  moan  temperature  for  these  months  was,  respectively,  58.67° 
and  55.3°  F. 

THE    LARVA. 

The  length  of  time  occupied  by  this  insect  in  the  larval  stage  dur- 
ing the  months  of  March,  April,  and  May  was  observed  during  the 
year  1911  by  confining  larvae  that  had  just  emerged  in  vials  con- 
stantly supplied  with  fresh  food.  Table  V  gives  the  results  of  these 
observations.  While  in  the  first  part  of  this  period  the  length  re- 
quired was  from  17  to  19  days,  later  it  was  shortened  to  9  and  11 
days.  The  average  mean  temperature  for  the  first  period,  March 
19  to  April  7,  was  61.5°  F.  and  for  May  14  to  May  27  it  was  61.1°  F. 


SEASONAL  HISTORY  AT   COMPTON,   CAL. 


33 


TABLE  V.— Length  of  larval  stage  of  the  bean  ///n'/w.  Compton,  Co?.,  March  and 
May,  1911. 


Date  larvae  hatched. 

Number 
of  larvae 
hatched. 

Larvae  pupating. 

Length  stage. 

Average 
mean 
temppra- 
ture. 

Date. 

Number. 

Minimum. 

Maximum. 

Mar.  19  

8 

7 
15 
14 

(Apr.    5 
{Apr.    ti 
Upr.     V 
May   24 
/May   26 
\Mav   27 
May   27 

».„ 

17 

10 

1        " 

Day,. 
19 

1        " 

11 

•jr. 

61.5 

62.1 
62.1 

May  14  

May  16 

May  18  

i  Kest  killed  by  heat. 

During  June  and  the  first  part  of  July  this  method  of  rearing 
larvae  to  secure  the  length  of  instars  was  repeated,  with  the  results 
shown  in  Table  VI. 

TABLE  VI. — Length  of  larval  stage  of  the  bean  thrii>*  in  June  and  the  firxt  part 
of  July,  1911,  Compton,  Cal. 


Exp. 

No 

Eggs  hatched. 

Larvae  pupated. 

Total 
pupated. 

Duration  of  stage.        A  verage 
mean 

Date. 

Number. 

Date. 

Number. 

Minimum. 

tempera- 
Maximum,       ture. 

1 
2 

June  15  

5 
-    50 

50 
50 

/June  28 
\July     1 
{July   10 
July   11 
July   12 
(July   11 
\July    12 
July    13 

1 

j 

4 
3 

2 

11 

11 
3 

Days. 
13 

11 

11 
12 

Days.            'F. 

:|  - 

June29  
June  29  

1 

Here  the  minimum  for  the  larval  stage  was  11  days  and  the  maxi- 
mum 14  days. 

In  July  larvae  were  reared  from  eggs  laid  in  normal  growing 
plants,  situated  in  an  outdoor  insectary  under  normal  conditions. 
These  experiments  are  all  given  in  Table  VII. 

TABLE  VII. Length  of  larval  stage  of  the  bean  thrip*  in  July,  1911,  at  Compton, 

Cal. 


Eggs  hatched. 

Date  and  number  of  larvae 

Total 
larvae 

Length  of  larval  stage. 

Average 
mean 

No. 

Date. 

Number. 

pupating. 

pupat- 
ing. 

Minimum. 

Maximum. 

ture. 

Day,. 

Days. 

•  F. 

1 

[July   23 
July   24 

5 

54 

)  July  31.  85  larvae  feeding;  Aug. 
I    2,  all  but  10  left  plant  to  pu- 

85 

10 

12 

e.8 

2 

ljuly  25 
July   24 
July  25 
July  26 

16 
26 
18 
9 

|     pate;  Aug.  5,  10  prepupae. 
(Aug.  2,  all  larvae  left  plant  to 
pupate  in  cracks.    These  lar- 
\    vae  were  feeding  from  7  to  9 
(    days  and  then  left  the  plant. 

68.8 

f 

3 

/July  28 
July  29 

8 
15 

Aug!  9,  number  of  larvae  pu- 
pated. 

11 

}         66'4 

34 


THE   BEAN    THKIPS. 


In  these  experiments  the  larvae  were  observed  to  feed  for  a  period 
of  9  to  10  days  and  then  to  leave  the  plant  to  pupate,  and  10  to  12 
days  were  required  between  hatching  from  the  egg  and  changing  to 
'prepupa?. 

During  the  year  1910  a  number  of  larvae  that  hatched  on  July  28 
were  observed  to  change  to  prepupjc  on  August  7,  the  total  length 
of  the  larval  stage  being  10  days,  with  an  average  mean  temperature 
of  72.1°  F. 

The  length  of  this  stage  later  in  the  summer  and  in  early  fall 
for  this  locality  unfortunately  was  not  observed,  but  was  probably 
somewhat  shorter  for  August  and  September  and  considerably 
longer  in  October  and  November. 

THE   PREPUPA   AND  PUPA. 

As  the  prepupa  and  pupa  are  two  distinct  stages,  although  closely 
related,  the  length  of  each  was  separately  determined.  These  two 
stages  during  the  spring  of  1911  required  from  3  to  6  days  for  the 
prepupa  and  from  9  to  14  days  for  the  pupa,  or  a  total  of  from  14 
to  19  days.  The  results  are  shown  in  Table  VIII,  with  the  average 
mean  temperature  for  each  experiment. 

TABLE  VIII. — Length  of  prepupal  and  pupal  stages  of  the  bean  thrips  at  Comp- 
ton,  C'dl.,  during  March  to  May,  1911. 


Larvse  changed  to  pre- 
pupa\ 

Prepupae 
changed  to 
to  pupae. 

Adults 
emerged. 

Length  of  stage. 

Average 

Exp 

Date. 

Num- 
ber. 

Date. 

Num- 
ber. 

Date. 

Num- 
ber. 

Pre- 
pupal. 

Pupal. 

Total. 

ture. 

Days. 

Days. 

Days. 

•P. 

1 

Mar.  31  

5 

Apr.     3 

5 

Apr.  17 

5 

3 

14 

17 

59.2 

2 

\pr  10 

1 

\pr    15 

\pr    24 

5 

9 

14 

59  5 

Apr.  19  

1 

Apr.  25 

j 

May     4 

1 

6 

9 

15 

57.9 

4 

Apr.  24  

2 

Apr.  29 

1 

May   10 

1 

5 

11 

16 

56.9 

Total  

9 

8 

8 

In  the  month  of  July  these  stages  required  from  1  to  4  days  for  the 
prepupa,  and  from  4  to  7  days  for  the  pupa,  or  a  total  of  from  5  to  11 
days.  The  number  that  required  less  than  7  days,  however,  was  very 
small.  During  this  month  the  average  mean  temperature  was  G9°  F. 

Table  IX  shows  the  results  of  these  experiments  and  the  average 
temperature  for  each. 


SEASONAL  HISTORY  AT   COMPTON,   CAL.  35 

TABLE  IX.— Length  of  prepupal  and  pupal  singes  of  the  bean  thrips  at  Comp- 
ton,  Cal.,  during  July,  J<)11. 


Erp. 

Changed  to  prepupa. 

Changed  to 
pupa. 

Adults 
emerged. 

Length  of  stage. 

Average 

No. 

Date. 

Num- 
ber. 

Date. 

Num- 
ber. 

Date. 

Num- 
ber. 

Pre- 
pupal. 

Pupal. 

Total. 

tempera- 
ture. 

Days. 

Days. 

Day,. 

•r. 

July  1  

7 

July     5 

7 

/July   11 
\July   12 

2 
5 

f        4 

6-7 

10-11 

71.7 

July  10  

3 

July   13 

3 

July   18 

3  '          3 

1 

8 

2 

July  11  

7 

/July   14 
\July  15 

6 

1 

Wy   IS 

7             3 

4 

7 

70.1 

July  13 

3 

/July  14 
\July  15 

1 
2 

|july   19 

1       ,-2 

4-5 

5-7 

3 

4 

/July  15  
\July  10  
July  19 

1 

2 
2 

July  17 
July  18 
July  23 
July   24 

1 
1 
2 

July  24 
July  24 
July  29 
July  29 

1 
1 

2 

2 

2 
2 
3 
3 

6 
6 
5 

9 
8 
9 

8 

71.8 
63.5 

July  20  

During  the  month  of  August,  1010,  at  Los  Angeles,  CaL,  larvae 
changed  to  prepupaj  August  2  and  the  adults  emerged  on  August  9, 
requiring  7  days  for  the  prepupal  and  pupal  stages.  For  this  period 
the  average  mean  temperature  at  Compton,  10  miles  out,  was  72.4°  F. 
Another  lot  changed  to  prepupa  on  August  7  and  the  adults  emerged 
on  August  15,  giving  a  total  of  8  days  for  the  prepupal  and  pupal 
stages.  The  average  mean  temperature  at  Compton  for  the  period 
was  71.4°  F. 

For  the  latter  part  of  August  and  for  September  the  length  of  these 
stages  is  nearly  that  required  in  July.  However,  in  October  this 
time  is  lengthened  to  some  extent,  Larvae  that  changed  to  prepupac 
on  November  3,  1910,  required  until  November  1C  before  the  adults 
emerged,  or  a  total  of  13  days.  The  average  mean  temperature  for 
the  period  was  59.9°  F. 

Records  made  of  the  length  of  the  prepupal  and  pupal  stages  for 
November  and  December  1910,  as  given  in  Table  X,  show  that  at 
that  time  of  year  the  period  required  was  greatly  prolonged,  the 
prepupal  stage  requiring  from  7  to  9  days  and  the  pupal  stage  from 
20  to  24  days,  making  a  total  period  of  from  27  to  33  days.  During 
this  period  the  mean  average  temperature  was  53.58°  F. 

TABIE  X—  Length  of  prepupal  and  pupal  ztagea  of  the  VK-HH  /ftri/w  for  \nrcmber, 
1910,  at  Compton,  Cal. 


Exp. 
No 

1 
2 

3 

Changed  to  prepupa. 

Changed  to  pupa. 

Adults  emerged. 

Length  of  stage. 

Date. 

Number. 

Date. 

Number. 

Date. 

Number. 

Pre- 
pupal. 

Pupal. 

Total. 

*~* 

27-29 

30-33 

Nov  14              

1 
2 

7 

Nov.  21 
Nov.  23 
(Nov.  25 
JNOV.  26 
t    or  27. 

1 
2 

4 
2 

Dec.   12 
(Dec.  13 
\Dec.  15 
Dec.  15 
Dec.  17 

1 
1 

1 
3 

*„„, 

\         7 
|        8-9 

»** 

20-22 

22-24 

Nov.  16  

Nov.17  
Total  

10 

9 

7 

36  THE   BEAN    THKIPS. 

TOTAL  LIFE  CYCLE. 

For  localities  with  climatic  conditions  similar  to  those  of  Compton, 
the  life  cycle  of  this  thrips  will  occupy  during  the  early  spring  about 
51  to  56  days,  taking  20  days  for  the  egg  incubation,  17  to  19  days 
for  the  larval  development,  and  14  to  17  days  for  the  prepupal  and 
pupal  stages. 

During  the  months  of  June  to  October  the  life  cycle  of  this  thrips 
will  occupy  from  28  to  43  days,  taking  13  to  18  days  for  the  egg 
stage,  10  to  14  days  for  the  larval  stage,  and  5  to  11  days  for  the 
prepupal  and  pupal  stages. 

During  the  rest  of  the  breeding  activity  the  life  cycle  must  be  even 
longer  than  in  the  spring,  as  in  November,  1910,  the  prepupal  and 
pupal  stages  alone  occupied  from  28  to  33  days,  so  that  for  the  de- 
velopment of  this  insect  during  October,  November,  and  the  first  of 
December  at  least  G8  to  73  days  must  be  required. 

EMERGENCE  FROM  HIBERNATION. 

In  1912  the  adults  began  to  emerge  from  hibernation  at  Holly- 
wood, Cal.,  in  January,  and  began  oviposition  at  once.  When  this 
locality  was  visited  on  February  7,  the  adults  were  found  to  be  feed- 
ing on  the  foliage  of  peas  and  beans  in  some  numbers.  They  were 
also  seen  in  copulation  in  many  cases.  A  careful  examination  dis- 
closed 4  young  larva?  feeding  on  bean  foliage,  so  that  the  adult  must 
have  laid  the  eggs  at  least  by  January  10.  This  fielcl  was  situated 
on  the  foothills  of  wThat  is  termed  a  frostless  belt,  and  it  may  be  that 
tins  insect  in  mild  winters  might  breed  there  during  the  entire 
period. 

On  February  17  adults  were  found  feeding  on  pea  foliage  in  Mis- 
sion Valley,  San  Diego  County,  but  no  young  wTere  seen.  February 
23  the  species  was  found  as  an  adult  feeding  on  pea  vines  in  the  truck 
farms  around  Los  Angeles,  and  on  March  13  adults  wrere  found  feed- 
ing in  small  numbers  at  Compton,  Cal.  From  then  on  the  adults  were 
common  feeding  on  different  plants,  but  not  until  April  17  were  the 
larva1  found  feeding  in  the  open  at  Compton,  although  they  were 
being  reared  in  the  open  insectary  at  that  place  from  material  col- 
lected at  Hollywood. 

It  would  probably  be  better  to  say  that  this  insect  begins  active 
reproduction  at  a  varying  time,  those  in  the  most  protected  places 
starting  as  early  as  January  10,  and  the  others  over  the  next  60  days. 
However,  during  the  early  spring  the  multiplication  and  spread 
seem  to  be  very  slow. 

ENTRANCE   INTO  HIBERNATION. 

As  the  month  of  October  appears,  the  adults  become  sluggish,  do 
less  feeding  and  lay  fewer  eggs,  and  apparently  many  enter  hiberna- 


SEASONAL   HISTORY  IN   THE  IMPERIAL  VALLEY.  37 

tion.  The  larvae  become  much  less  numerous  and  require  an  extended 
period  to  complete  their  growth.  In  1910  the  last  larvae  in  numbers 
were  observed  in  the  field  on  November  20,  while  one  was  observed  on 
December  1,  and  three  on  December  13,  and  during  the  first  part  of 
December  these  had  all  changed  to  pupae  or  died.  The  last  adult 
appeared  on  December  27.  In  1911  the  larvae  were  not  very  abundant 
after  the  first  week  in  October,  and  the  last  ones  were  observed  in 
Los  Angeles  County  on  November  21. 

NUMBER   OF   GENERATIONS. 

In  the  section  of  the  State  in  which  this  insect  was  under  observa- 
tion, the  first  spring  generation  may  commence  as  early  as  January 
10  and  probably  egg-laying  by  overwintering  adults  continues  for  a 
considerable  time.  As  the  period  of  oviposition  is  quite  extended  the 
different  broods  tend  to  overlap ;  still  in  midsummer  there  are  certain 
periods  when  the  majority  of  thrips  present  may  be  adults  or  larvae. 
Up  to  April  1  there  is  probably  one  small  full  generation  occupying 
about  56  days.  During  April  and  May  a  second  generation  will 
develop;  then  during  the  four  months  of  June,  July,  August,  and 
September  there  is  one  full  generation  for  each  month.  For  the  rest 
of  the  period  of  the  breeding  activity  we  have  probably  a  partial 
brood  that  extends  over  68  to  73  days. 

Thus  during  the  year  this  insect  has  a  small  generation  in  both  the 
early  spring  and  late  fall  and  five  full  generations  during  the  rest  of 
the  time,  or  seven  generations  a  year. 

SEASONAL  HISTORY  IN  THE  IMPERIAL  VALLEY. 

The  observations  on  the  life  cycle  of  this  insect  for  Imperial  Valley 
were  conducted  by  Mr.  V.  L.  Wildermuth  at  El  Centre,  Cal.,  in  1910. 

EGG  PERIOD. 

Mr.  Wildermuth  confined  adults  in  vials  with  fresh  sprigs  of 
alfalfa  and  kept  the  foliage  fresh  by  wrapping  the  stems  in  moist 
cotton  until  the  larvae  hatched  from  the  eggs.  While  many  eggs  were 
secured  by  this  method,  large  numbers  died  before  hatching,  as  the 
foliage  became  too  dry.  but,  as  shown  in  Table  XI,  the  egg  stage 
varied  from  four  days  in  a  single  case  to  five  days  in  a  lot  of  20  eggs 
laid  the  last  day  of  August.  The  length  of  the  egg  stage  at  that 
locality  was  only  one-third  as  great  as  that  observed  by  the  writer  in 
Los  Angeles  County,  but  this  is  clue  in  a  large  measure  to  the  high 
temperature  of  the  Imperial  Valley. 


243602 


38 


THE   BEAN    THRIPS. 


TABLE  XI. — Length  of  incubation  of  the  eggs  of  the   lean  thrips,  El  Centra, 

Co?.,  1910. 


Dateofoviposition. 

Number 
laid. 

Eggs  hatched. 

Length 
of  stage. 

Average 
mean 
tempera- 
ture. 

Date. 

Number. 

2 

(2) 
.(2) 

Aug.    1 

Aug.  is 

Sept.    6 

2 

1 
20 

D«^ 

5 

"&.! 

»88.7 

Aug.  11  

Records  missing. 


Many. 


3  At  Brawley. 


LARVAL,   PERIOD. 

The  active  feeding  larva  molts  once  before  its  final  molt  to  the 
prepupal  stage.  This  occurs  in  from  one  and  one-half  to  two  days 
after  it  hatches  from  the  egg.  The  larva  becomes  full  grown  and 
changes  to  the  prepupa  in  from  four  and  one-half  to  five  days.  As 
might  be  expected  from  the  great  difference  in  the  incubation  period 
of  the  egg,  the  larval  period  in  the  Imperial  Valley,  as  observed  by 
Mr.  Wildermuth,  is  much  shorter  than  at  Compton.  These  data 
are  given  in  Table  XII. 

TABLE  XII. — Length   of   larval   stage   of   the   bean   thrips   at   El   Centro,   Cat., 
during  1910. 


Eggs  hatched. 

Molted. 

Changed  to 
prepupa. 

Length. 

Average 
mean 

Date. 

Number. 

Date. 

Number. 

Date. 

Number. 

ature. 

Days. 

°F. 

Aug.  15  
Aug.  18  
Aug.  26  

Aug.  16 
Aug.  19 
Aug.  28 

Aug.  19 
Aug.  22 
Aug.  31 

1 

85.8 

(1)9i.o 

Sept.l  
Sept.  22  

Sept.    3 
Sept.  24 

Sept.    5 
Sept.  27 

4 
5 

89.7 
81.8 

Total  

7 

5 

5 

1  Records  missing. 


PREPUPAL  AND  PUPAL  PERIODS. 


Unfortunately  Mr.  Wildermuth's  records  give  a  very  small  amount 
of  data  on  the  length  of  the  prepupal  and  pupal  periods.,  but  in  the 
six  examples  observed  (see  Table  XIII)  the  stages  varied  from  2 
to  3  days.  While  the  writer  was  studying  the  greenhouse  thrips 
the  prepupal  stage  was  often  observed  to  last  only  a  few  hours,  and 
this  same  condition  probably  occurs  with  the  present  species  in  the 
high  temperature  of  the  Imperial  Valley. 


HIBERNATION.  39 

TABLE  XIII.— Length  of  prepupal  and  pupal  stages,  El  Centra,  CaL,  1910. 


Exp. 
No. 

Date  changed  to  prepupa. 

Date 
adult 
emerged. 

Length 
of 
period. 

Average 
mean 

t'-:ri;  .  r- 
ature. 

1 

Aug  19 

Days. 
2*-3 

'F. 

2 

Aug.  22  

AUK  24 

2J-3 

B 

3 

Sept.  6  

Sept     8 

2-24 

'849 

4 

Sept.  4 

<!•',!          S 

3 

*85  1 

5 

Sept  7 

Sept    9 

2 

*  87  0 

6 

Sept.  27  

Sept  29 

2J 

(') 

1  Records  missing. 


'  Temperature  at  Brawley,  U.  S.  Weather  Bureau. 


In  the  Imperial  Valley  the  egg  stage  is  from  4i  to  5  days,  the 
larval  stage  from  4  to  5  days,  and  the  prepupal  and  pupal  stages 
from  2  to  3  days,  making  the  total  life  cycle  only  10  to  12£  days 
during  the  extreme  summer  temperature. 

The  eggs  were  deposited  within  2  days  from  the  time  the  adult 
females  emerged,  so  that  a  new  generation  might  occur  every  14 
days  in  midsummer.  If  the  insect  -emerges  from  hibernation  in  the 
Imperial  Valley  at  the  same  time  as  in  Compton,  there  will  un- 
doubtedly be  1  generation  in  the  early  spring  occupying  30  to  40 
days,  and  then  2  generations  a  month  for  5  or  6  months  and  1 
longer  generation  in  the  fall,  or  12  to  14  generations  a  year.  Indeed, 
with  such  rapid  multiplication  it  is  not  strange  that  crops  in  the 
late  fall  become  seriously  infested. 

SEASONAL   HISTORY   AT   TEMPE,    ARIZ. 

Mr.  Wildermuth  during  October  and  November,  1911,  made  some 
observations  on  the  life  cycle  of  this  thrips  at  Tempe.  These  gave 
a  life  cycle  of  very  nearly  the  same  duration  as  in  the  Imperial  Valley 
in  the  warm  weather,  but  in  November  the  cycle  was  lengthened 
considerably.  He  found  that  specimens  collected  as  larvae  on  October 
30  did  not  emerge  as  adults  until  December  1.  This  shows  the  same 
effect  of  cooler  weather  on  this  insect  that  the  writer  observed  at 
Compton,  Cal. 

Taking  the  results  of  Mr.  Wildermuth's  and  the  writer's  observa- 
tions on  the  bean  thrips,  there  is  a  minimum  life  cycle  of  10  days 
where  the  "average  mean  temperature  is  about  88.75°  F.,  and  a  maxi- 
mum of  about  73  days  with  an  average  mean  temperature  of  about 
53.58°  F. 

HIBERNATION. 

This  insect  hibernates  as  an  adult  only,  through  most  of  its  dis- 
tribution at  least.  It  may  be  that  in  the  more  southern  portions  of 
its  range  it  breeds  continuously  throughout  the  year,  but  our  obser- 
vations in  these  localities  mentioned  have  failed  to  show  it 


40  THE   BEAN    THRIPS. 

In  the  section  around  Compton,  CaL,  the  adults  were  found  to 
hibernate  in  small  numbers  on  the  underside  of  leaves  of  nasturtium, 
sugar  beets,  wild  heliotrope,  and  other  plants.  They  were  also  found 
hiberating  in  some  numbers  in  dead  leaves  and  rubbish.  When  dis- 
turbed they  were  sluggish  and  made  little  effort  to  escape. 

Mr.  P.  R.  Jones  (in  litt.)  says  that  around  Lindsay,  CaL,  the  adults 
hibernate  in  numbers  in  the  navel  end  of  the  Washington  navel 
orange.  He  also  stated  that  in  midwinter  he  had  taken  this  thrips 
along  creek  beds  hibernating  on  the  underside  of  leaves  of  wild  rasp- 
berry and  blackberry  which  were  still  on  the  plants. 

NOTES   ON   OCCURRENCE. 

Apparently  the  different  methods  of  cultivation  bear  strongly  on  the 
abundance  of  these  insects  and  consequent  injury  they  may  cause  to  a. 
crop.  In  Los  Angeles  County,  where  clean  cultivation  is  not  strictly 
followed  out,  it  begins  to  breed  in  the  spring  on  the  wild  food  plants 
and  increases  more  and  more  until  in  August  it  has  reached  enormous 
numbers.  Before  this  the  native  plants  are,  many  of  them,  either 
matured  or  destroyed  by  the  thrips,  and  as  a  result  it  spreads  more 
and  more  to  the  cultivated  crops  and  trees  that  serve  as  hosts.  Dur- 
ing some  years  this  occurs  late  in  the  season  and  very  little  real 
damage  results,  but  if  this  insect  should  begin  the  year  in  fairly  large 
numbers  and  under  favorable  conditions,  great  damage  may  result. 

In  Ventura  County,  in  October,  1910,  the  author  made  a  careful 
examination  of  the  entire  bean-growing  section  and  found  that  the 
bean  thrips  occurred  in  extremely  small  numbers  on  the  little  vege- 
tation remaining.  At  the  same  time  it  was  extremely  abundant 
around  Compton.  This  condition  seemed  to  be  a  direct  result  of  the 
practice  of  the  growers  in  Ventura  of  thoroughly  plowing  and  culti- 
vating the  fields  within  a  short  time  after  the  beans  are  harvested 
and  keeping  them  in  perfect  condition  until  the  next  crop  is  planted. 
This  advantage  is  increased  because  there  is  very  little  waste  space 
where  weeds  can  grow  up.  Our  investigations  during  the  past  two 
years  have  shown  that  this  insect  is  not  abundant  on  cultivated  crops 
in  the  spring  or  early  summer,  but  that  after  this  period  it  increases 
more  and  more,  and  in  certain  years  injures  them  so  severely  as  to 
cause  much  loss. 

NATURAL   CONTROL. 

RAINS. 

One  of  the  largest  factors  in  the  destruction  of  thrips  in  some 
localities  is  the  prevalence  of  hard,  dashing  rains.  The  author, 
while  working  in  Florida  with  the  greenhouse  thrips,  once  observed 


NATURAL   CONTROL.  41 

that  crotons,  which  in  the  greenhouse  were  infested  with  thousands 
of  thrips  and  which  in  June  were  placed  outside  and  subjected  to 
the  Florida  summer  rains,  when  examined  in  September  were  so  free 
from  this  insect  that  it  was  almost  impossible  to  find  specimens, 

California,  with  its  long  dry  season,"  does  not  obtain  the  same* 
benefit,  but  even  there  the  rains  may  reduce  attacks  of  the  bean  thrips 
to  some  extent.  On  February  7,  1911,  the  writer  observed  a  pea 
field  that  had  from  5  to  8'  adults  on  every  plant.  After  this  date 
there  was  a  severe  rain  of  several  days'  duration,  and  when  the 
field  was  again  examined,  on  April  1,  it  was  almost  impossible  to 
find  the  thrips.  Mr.  Graf,  writing  from  Puente,  Cal.,  on  October  6, 
1911,  noted  that  the  larvae  were  much  scarcer  than  a  week  earlier, 
probably  owing  to  a  rainfall  of  one-half  inch.  Mr.  Wildermuth, 
at  Tempe,  Ariz.,  wrote  on  October  5,  1911 : 

A  search  in  the  patch  of  alfalfa  back  of  the  office,  where  thrips  had  been 
very  numerous  for  several  weeks,  failed  to 'reveal  very  many  thrips  to-day. 
The  heavy  raiu  of  yesterday  and  last  night  was  probably  responsible  for 
washing  them  off. 

In  California,  then,  late  rains  in  the  spring  may  greatly  diminish 
the  numbers  of  this  insect,  or  early  rains  in  the  fall  destroy  many 
that  otherwise  would  enter  hi- 
bernation. 


NATURAL    ENEMIES. 

FIG.  10. — The  bean  thrips :  Prepupir  parasit- 


A  great  deal  of  attention  has 
been   given   to   the    subject    of 
natural  enemies  and  some  information  obtained  on  this  important 
feature  of  insect  control. 

In  the  fall  of  1910  the  larva  of  this  thrips  was  discovered  to  be 
parasitized  (see  fig.  10)  by  a  minute  hymenopteron.  This  was  de- 
scribed by  Mr.  J.  C.  Crawford  as  Thripoctenus  ru$selli  (see  fig.  11). 
During  1911  this  parasite  was  observed  to  work  extensively  in  Los 
Angeles  County  on  the  bean  thrips  and  seemed  to  destroy  large 
numbers.  Some  collections  of  thrips  larvae  gave  as  high  as  70  per 
cent  killed  by  the  parasite.  For  a  full  account  of  this  parasite  the 
reader  is  referred  to  Technical  Series  23,  Part  II,  Bureau  of  Ento- 
mology, United  States  Department  of  Agriculture. 

During  1911  the  larva  of  a  green  lacewing  fly   (Chrysopa  cal 
fornica  Coq.)  was  commonly  observed  feeding  on  the  larva  of  this 
thrips.     As  this  insect  was  observed  so  engaged  in  several  localities 
in  Los  Angeles  County,  and  in  noticeable  numbers,  it  probably  k 
a  large  number  of  thrips. 

The  larva  of  a  syrphid  fly  (Sphayrophoria,  sulphuripes  Thou  m) 
wa's  also  observed  on  numerous  occasions  feeding  on  the  larva  of 


42 


THE   BEAN    THRIPS. 


the  bean  thrips,  and  in  confinement  larvae  were  observed  to  kill  and 
eat  large  numbers  of  the  host. 

The  young  of  Triphleps  insidiosus  Say  were  noticed  on  many 
occasions  feeding  on  the  young  of  this  thrips  and  undoubtedly  aid 
*in  reducing  its  numbers. 

The  larva?  and  adults  of  Hippodamia  convergent  Guer  were  fre- 
quently collected  on  plants  infested  with  thrips,  where  they  were 
busily  engaged  in  feasting  on  the  tender  larva?  of  the  bean  thrips. 

On  several  occasions  larvas  of  a  predaceous  thrips,  probably  /Eolo- 
thrips  fasciatus  L.,  when  collected  were  feeding  on  the  Iarva3  of  the 
bean  thrips. 


parasite,    Thripoctenus    runm-lli:   Adult. 
(Author's  illustration.) 


Greatly    enlarged. 


Mr.  1*.  R.  Jones  informed  the  writer  that  at  Lindsay,  Cal.,  in 
1910,  he  found  a  "  nematode  parasite  working  in  the  full-grown 
larva*  of  the  bean  thrips." 

A  curious  circumstance  in  connection  with  the  observations  made 
on  the  natural  enemies  of  the  bean  thrips  was  the  fact  that  in  all  of 
the  predaceous  forms  noted  the  alimentary  tract  became  bright  red, 
undoubtedly  due  to  the  crimson  or  reddish  pigmentation  of  the  host. 

ARTIFICIAL   CONTROL. 
CULTURAL    METHODS. 

Iii  the  case  of  crops  planted  over  large  areas  and  difficult  or  im- 
possible to  spray,  such  as  beans,  alfalfa,  or  cotton,  cultural  methods 
offer  the  most  hope  as  a  remedy  for  the  bean  thrips.  Where  this 
insect  threatens  injury  it  is  recommended  that  these  methods  be  used 
so  far  as  possible.  It  is  very  important  that  the  crops  be  given 


ARTIFICIAL  CONTROL.  43 

careful,  clean  cultivation,  so  that  all  weeds  may  be  kept  down  in 
the  fields  at  all  times,  including  the  spring  and  fall.  These  same 
weeds,  especially  the  different  species  of  wild  lettuce,  should  be  care- 
fully destroyed  along  the  edges  of  all  fields  and  fence  corners  and 
along  the  roads  and  railroad  tracks.  Cotton  and  beans  should  not 
follow  in  old  alfalfa  fields  if  the  latter  were  badly  infested  with  the 
bean  thrips,  and  fields  of  these  crops  should  be  removed  as  far  as 
possible  from  the  alfalfa  fields.  They  should  also  be  planted  as 
early  as  is  consistent  with  good  farming  and  encouraged  by  fre- 
quent cultivations  and  fertilizers  where  necessary  to  produce  an  early 
crop  so  as  to  escape  the  ravages  of  the  bean  thrips  in  the  late  summer. 

As  this  insect  feeds  on  such  a  variety  of  plants  it  is  hardly  pos- 
sible that  rotation  of  crops  would  aid  materially  in  its  control  unless 
some  crop  could  be  found  that  is  quite  immune. 

Where  it  is  injuring  alfalfa  Mr.  Wildermuth  recommends  disking 
and  thorough  renovation  of  the  fields  and  good  irrigation  in  order 
to  give  the  plants  as  much  chance  as  possible  to  make  a  quick  growth. 

SPRAYING. 

The  control  of  this  thrips  by  spraying  is  impracticable  for  a  crop 
such  as  alfalfa  or  cotton,  and  because  of  the  low  trailing  vines  of 
the  bean  will  probably  be  successful  with  this  plant  only  when  the 
vines  can  be  easily  reached  from  the  underside.  In  case  injury  to 
fruit  trees  is  threatened  it  can  be  controlled  by  using  the  spray  so 
successful  against  the  pear  thrips.  This  is  a  solution  of  2|  per  cent 
nicotine,  diluted  at  the  rate  of  1  part  to  60  parts  of  water  in  a  6 
per  cent  distillate-oil  emulsion.1 

The  distillate-oil  stock  emulsion,  according  to  the  formula  of 
Foster  and  Jones,  is  made  as  follows : 

Hot  water -gallons..     12 

Fish-oil  or  whale-oil  soap 

Distillate-oil   (raw)  30°  to  34°  Baum6 — 

Have  the  water  boiling  hot  when  put  into  the  spray  tank  and  add  the  soap 
immediately  while  the  agitator  is  running  at  a  good  speed.  When  the  soap  Is 
all  thoroughly  dissolved  pour  in  the  oil  slowly,  keeping  the  mixture  well  agi- 
tated while  the  oil  is  going  into  the  tank.  When  all  of  the  oil  is  in  and  well 
mixed,  pump  out  through  the  nozzles  at  good  pressure  (not  less 
pounds)  into  storage  tanks. 

No  one  should  attempt  to  make  this  stock  emulsion  without  a  power  spra 
machine,  as  thorough  agitation  and  high  pressure  are  important   requisil 
Also   care  should  be  used  in  having  measurements  reasonably  exact,  the  water 
boiling  'hot    and  the  soap  thoroughly  dissolved  before  any  oil  is  put  In.    1 
stock  solution  contains  approximately  55  per  cent  oil,  and  to  make  a  3  per  c< 
emulsion  use  5*  gallons  of  this  stock  in  each  100-gaIlon  tank. 

i  For  a'  full  account  of  this  spray  as  used  against  the  pear  thrips.  see  Circular  131, 
Bureau  of  Entomology,  U.  S.  Dept.  of  Agriculture,  pp.  8-0. 


44  THE   BEAN    THEIPS. 

A  simpler  formula  and  one  that  possibly  will  act  quite  as  well  on 
this  insect,  where  it  is  exposed  on  the  foliage,  and  one  that  will  offer 
no  chance  for  the  burning  of  the  foliage,  has  given  good  results  in 
the  destruction  of  Heliothrips  rubrodnctus  Giard  in  Florida.  Mr. 
Edward  Simmonds,  of  the  Bureau  of  Plant  Industry,  advised  the 
writer  that  a  solution  composed  of  1  gallon  of  blackleaf  tobacco  ex- 
tract, 1  pound  of  whale-oil  soap,  and  50  gallons  of  water  gave  excel- 
lent results  in  treating  trees  infested  by  this  insect.  This  formula 
seems  a  little  strong  to  the  writer  and  he  would  recommend  using  the 
blackleaf  at  the  rate  of  1  part  to  60  parts  of  water.  In  the  place  of 
this,  a  40  per  cent  solution  of  nicotine  can  be  substituted  at  the  rate 
of  1  part  to  from  1.000  to  2,000  parts  of  water-. 

DISTRIBUTING   THE   PARASITE. 

Possibly  the  parasite  of  this  insect  can  be  artificially  distributed 
with  good  results  to  sections  infested  by  this  thrips  where  the  para- 
site does  not  occur.  For  directions  and  methods  of  shipping  this 
parasite,  the  reader  is  referred  to  Technical  Series  23,  Part  II,  Bureau 
of  Entomology.  U.  S.  Department  of  Agriculture,  page  51. 

BIBLIOGRAPHY. 

:1.  I'ERGANDE,  THEODOHE. — Insect  Life,  vol.  7,  pp.  391-392,  1895. 
Original   description   of  the   species. 

'1.  UZEL,  ,T. — Mon.  der  Orel.  Thysan.,  p.  459,  1S95. 

Copy  of  the  original  description  of  Pergande. 

:',.   HJNDS,  W.  E.— Proc.  IT.  S.  X^it.  Mus.,  vol.  26,  pp.  174-175.  3902. 
Redescription  of  single  female. 

4.  DANIEL,  S.  M.— Ent.  News,  vol.  15,  p.  294,  3904. 

This  author  seems  to  have  taken   Pergande's  records  of   locality  and  host 
of  this  insect. 

5.  DANIEL,  S.  M.— Ent.  News,  vol.  15,  p.  297,  1904. 

Described  the  male  as  a  new  species  under  the  name  Caliothrips  woodicorthi. 
<;.  Mon/rox,  DUDLEY. — Tech  Ser.  12,  Bur.  Ent.,  U.  S.  Dept.  Agr.,  pp.  39,  43, 
51,  52.     PL  II,  figs.  12-14,  1907. 

Records  capture  on  orange,  pea  vines,  and  wild  vetch  and  places  Caliothrips 
ivoodworthi  as  a  synonym  of  H.  Jasciatus. 

7.  CRAWFORD,  D.  L. — Pomona  Journ.  Ent.,  vol.  1,  pp.  120-121,  1909. 

Records  this  species   from   pine   foliage,   Lotus  {/laber,  and  blossom   end  of 
ripe  apple  in  southern  California. 

8.  BREMNER,  O.  E. — Destructive  insects  and  their  control.     <Cal.  State  Corniu. 

Hort,  1910. 

This  thrips,  under  the  name  Euthrips  fasciatus,  was  recorded  as  injuring 
peas  and  beans  and  occurring  on  alfalfa  and  peach  and  pear  trees. 

n.  COIT,  .1.  ELIOT,  and  PACKARD,  W.  E.— Cal.  Agr.  Exp.  Sta.,  Bui.  210,  pp.  168. 
184,  1911. 

This  thrips,  under  the  name  Heliothrips  fascietns  (sic),  recorded  as  injuring 
alfalfa  and  cotton  in  the  Imperial  Valley,  Cal. 

10.  MOULTON,  DUDLEY.— Tech.  Set.  21,  Bur.  Eiit.,  U.  S.  Dept  Agr.,  pp.  9,  14, 
23-24. 

Notes  on  synonymy  and  food  plants. 


BIBLIOGRAPHY.  45 

11.  KARNY,  H. — Entomologische  Rundsckuit,  Jahrgang  28.  p.  180,  1911. 

Revision  of  the  genus  Heliothrips,  with  table  of  species  Including  fcuciatm. 

12.  RUSSELL,  H.  M.— Proc.  Ent.  Soc.  Wash.,  vol.  12,  pp.  235-238,  1911. 

A  brief  summary  account  of  a  parasite  reared  from  Heliothrips  fasciatus. 
33.  RUSSELL,  H.  M.— Tech.  Ser.  23,  Pt.  II,  Bur.  Ent.,  I*.  S.  Dept.  Agr..  pp.  ur.  r,-j. 
3912. 

A  very  full  account  of  the  life  history  and  habits  of  the  parasite  reared  from 

this  thrips. 

14.  MOBRILL,  A.  W. — Monthly  Bui.  State  Hort.  Comm.  Cal..  vol.  1,  no.  5.  p.  H52, 
April,  1912 

Heliothrips   fasciatus   Perg.    is   noted   as   one   of   the   species   affecting    the 
orange. 


INDEX. 


.Eolothripsfasdatus,  probable  enemy  of  bean  thrips 42 

Alfalfa,  food  plant  of  bean  thrips 16, 17, 28-30 

Apple,  food  plant  of  bean  thrips 16  31 

crab,  bean  thrips  taken  thereon 17 

Atnplex  sp.,  food  plant  of  bean  thrips 31 

Beans,  food  plant  of  bean  thrips 16, 27 

Beets,  sugar,  food  plant  of  bean  thrips 17, 28 

table,  food  plant  of  bean  thrips 28 

Bidens  pilosa,  food  plant  of  bean  thrips 31 

Cabbage,  food  plant  of  bean  thrips 28 

Caliothrips  woodwort.hi,  bibliographic  references 44 

synonym  of  Helioihrips  fasdatus •. 16 

Cauliflower,  food  plant  of  bean  thrips 28 

Chenopodium  murale,  food  plant  of  bean  thrips 31 

Chrysomphalus  aurantii,  association  with  bean  thrips  on  orange  leaf 16 

Chrysopa  calij "arnica,  enemy  of  bean  thrips 41 

Cigarette  flower,  Chinese.     (See  Nicotiana  gJauca.) 

Clover,  burr,  food  plant  of  bean  thrips 31 

Cotton,  food  plant  of  bean  thrips 16, 17, 28-30 

Crepsis  (?)  sp.,  food  plant  of  bean  thrips 31 

Cultural  methods  in  control  of  bean  thrips 42-43 

Distillate-oil  emulsion  against  bean  thrips 43 

Echinocystis,  probable  food  plant  of  bean  thrips 31 

Erigeron  canadensis,  food  plant  of  bean  thrips 31 

Eunanus  brevipes,  food  plant  of  bean  thrips 31 

Euryptera  lucida,  food  plant  of  bean  thrips 31 

Euthripsfasciatm,  bibliographic  reference 44 

=HeHothripsfasciatus 16 

pyri.     (See  Thrips,  pear.) 
Fish-oil  soap.     (See  Soap,  whale-oil.) 

Gnaphalium  calif ornicum,  food  plant  of  bean  thrips 31 

Helianthus  annuus,  food  plant  of  bean  thrips 31 

Helioihrips  fasciatus.    (See  Thrips,  bean.) 

hsemorrhoidalis,  larval  habits 

rubrocinctus,  control  by  spraying 44 

larval  habits 9 

Heliotrope,  wild.     (See  Heliotropium  curassavicum.) 

Heliotropium  curassavicum,  food  plant  of  bean  thrips 

Hippodamia  convergens,  enemy  of  bean  thrips 

Lacewing  fly,  green.     (See  Chrysopa  calif ornica.) 
Lactuca  scariola.     (See  Lettuce,  spiny  wild.) 

Lettuce,  food  plant  of  bean  thrips 

spiny  wild,  food  plant  of  bean  thrips 

47 


48  THE    BEAN    THHIPR. 

Page. 

Lotus  americanus,  food  plant  of  bean  thrips 31 

glaber,  food  plant  of  bean  thrips 16,  31 

Mirabilis  calif ornica,  food  plant  of  bean  thrips 31 

Nasturtium.     (See  Tropasolum  major.) 

Nematode  parasite,  enemy  of  bean  thrips 42 

Nicotiana  glauca,  food  plant  of  bean  thrips 31 

Nicotine  solutions,  against  bean  thrips 16 

sulphate  against  bean  thrips 16 

Oil.     (See  Distillate  oil  and  Soap,  Whale-oil.) 

Orange,  food  plant  of  bean  thrips 31 

Chrysomphalus  aurantii 16 

medium  in  dispersion  of  bean  thrips 15 

Parasite  of  bean  thrips,  artificial  distribution 44 

Peach,  food  plant  of  bean  thrips 16,  31 

Pea,  food  plant  of  bean  thrips 14.  16,  28 

wild.     (See  Lotus  americanus.) 

Pear,  food  plant  of  bean  thrips 16.  17,  28 

Pine,  food  plant  of  bean  thrips 16 

Polygonum  aviculare,  food  plant  of  bean  thrips 31 

Poplar,  tulip,  bean  thrips  found  thereon 31 

Potato,  food  plant  of  bean  thrips 28 

Radish,  food  plant  of  bean  thrips 31 

Rains  in  control  of  bean  thrips 40-41 

Soap,  whale-oil,  and  blackleaf  tobacco  extract  against  Heliothrips  rubrocinctus 

and  bean  thrips 44 

Sonchus  oleraceus,  food  plant  of  bean  thrips 31 

S phscrophoria  sulphuripes,  enemy  of  bean  thrips 41-42 

Tacsonia  mellissimus,  food  plant  of  bean  thrips 31 

Thistle,  sow.     (See  Sonchus  oleraceus.) 

Thripoctenus  russelli,  artificial  distribution 44 

parasite  of  bean  thrips 16, 41, 42 

Thrips,  bean,  adult  female,  description 9 

habits 17-23 

male,  description 10 

adults,  recently  described,  description 10 

bibliography 44-45 

control,  artificial 42-44 

natural 40-42 

description 8-9 

distribution 14-16 

egg,  description 10 

hatching 23-25 

stage,  length  at  Compton,  Cal 31-32 

in  Imperial  Valley 37-38 

enemies,  natural 41-42 

feeding  habits 20-21 

flight 21 

food  plants 27-31 

generations,  number,  at  Compton,  Cal 37 

habits  of  adult 17-23 

larva 23-26 

prepupa  and  pupa 26-27 

hatching  of  eggs 23-25 


INDEX.  49 

Thrips,  bean,  hibernation 

emergence  therefrom,  at  Compton,  Cal 36 

entrance,  at  Compton,  Cal 36-37 

in  navel  end  of  orange 

-,.,                                                                                   ' JD 

history j  g 

injury,  nature  and  extent g 

larva,  first-stage,  description 10-11 

habit8 :..""!!";;;""";;!;  23-26 

moltmg :..  25-26 

second-stage,  description j j 

larval  period,  length  at  Compton,  Cal 32-34 

in  Imperial  Valley 38 

taping f ""i 

length  of  life  in  winter 22-23 

normal 

life  cycle,  total  length  at  Compton,  Cal .,,,  35 

mating,  method j7_lg 

molting  of  larva 25-26 

nymph,  full  grown.     (See  Thrips,  bean,  pupa.) 
young.     (See  Thrips,  bean,  prepupa.) 

occurrence,  notes 40 

origin '- ......'..'.  14-16 

oviposition,  method  and  time 18-19 

number  of  eggs  deposited 19-20 

period 1 9_20 

prepupa,  description 12 

habits 20-27 

prepupal  period,  length  at  Compton,  Cal 34-35 

in  Imperial  Valley 38-39 

pupa,  description 13 

habits 26-27 

pupal  period,  length  at  Compton,  Cal 34-35 

in  Imperial  Valley 38-39 

recent  records 16-17 

reproduction,  kinds 20 

seasonal  history  at  Compton,  Cal 31-37 

Tempe,  Ariz 39 

in  Imperial  Valley 37-39 

sexes,  proportion 20 

greenhouse.     (See  Heliothrips  haemorrhoids!.*.  > 

pear,  destructiveness  in  California 7 

Tobacco  extract,  blackleaf,  and  whale-oil  soap,  against  Heliothrips  rubrodnctus 

and  bean  thrips 44 

Tomato,  food  plant  of  bean  thrips 28 

Triphleps  insidiosus,  enemy  of  bean  thrips 42 

Tropxolum  major,  food  plant  of  bean  thrips 31 

Tulip  poplar,  bean  thrips  found  thereon 31 

Turnip,  wild,  food  plant  of  bean  thrips ' 31 

Verbascum  virgatum,  food  plant  of  bean  thrips 31 

Vetch,  wild,  food  plant  of  bean  thrips 31 

Whale-oil  soap.     (See  Soap,  whale-oil.) 

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